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Hi and Flat-Field Problem

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  • Greg Crawford
    Hi Everyone, I recently purchased Ron s book and thought I had better join the list. Can I kick off with a question about a flat-field problem I am having? I
    Message 1 of 30 , Jun 10, 2002
      Hi Everyone,

      I recently purchased Ron's book and thought I had better join the list.

      Can I kick off with a question about a flat-field problem I am having? I use
      lightbox flats and lately have found that the image reduction in CCDSoftV5
      leaves traces of a negative image of the flat-field on the light frame after
      auto-reduction. You can see what I mean here:

      http://www.nelsonbay.com/~gc/Publication2.htm

      I have exposed the flat-fields for 2 seconds, which is enough to make the
      maximum pixel value about 20,000, which is approximately one third of my maximum
      of 65535 on an ST9E. The strange flat-field comes from having an AO-7 in the
      optical train.

      Can anyone suggest what is causing the problem?

      Greg Crawford
      Observing from Southern Skies

      *

      * *
      *


      *

      http://www.nelsonbay.com/~gc/observatory.htm

      "Though my soul may set in darkness, it will rise in perfect light,
      I have loved the stars too dearly to be fearful of the night."
      - from the gravestone of astronomer, John Brashear.



      ______________________________________
      Scanned and protected by Inflex
      http://pldaniels.com/inflex
    • spanish chris
      If you upload the original fits files, I will run them through Cadet and Pictorview, (the programs I use) to see if it is CCDSoft that is causing the problem.
      Message 2 of 30 , Jun 10, 2002
        If you upload the original fits files, I will run them through Cadet and Pictorview, (the programs I use) to see if it is CCDSoft that is causing the problem.

        Chris
        www.freewebz.com/spanishchris
        ----- Original Message -----
        From: Greg Crawford
        To: 'CCD NewAstro List'
        Sent: Monday, June 10, 2002 3:11 PM
        Subject: [ccd-newastro] Hi and Flat-Field Problem


        Hi Everyone,

        I recently purchased Ron's book and thought I had better join the list.

        Can I kick off with a question about a flat-field problem I am having? I use
        lightbox flats and lately have found that the image reduction in CCDSoftV5
        leaves traces of a negative image of the flat-field on the light frame after
        auto-reduction. You can see what I mean here:

        http://www.nelsonbay.com/~gc/Publication2.htm

        I have exposed the flat-fields for 2 seconds, which is enough to make the
        maximum pixel value about 20,000, which is approximately one third of my maximum
        of 65535 on an ST9E. The strange flat-field comes from having an AO-7 in the
        optical train.

        Can anyone suggest what is causing the problem?

        Greg Crawford
        Observing from Southern Skies

        *

        * *
        *


        *

        http://www.nelsonbay.com/~gc/observatory.htm

        "Though my soul may set in darkness, it will rise in perfect light,
        I have loved the stars too dearly to be fearful of the night."
        - from the gravestone of astronomer, John Brashear.



        ______________________________________
        Scanned and protected by Inflex
        http://pldaniels.com/inflex


        To unsubscribe from this group, send an email to:
        ccd-newastro-unsubscribe@egroups.com



        Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.



        [Non-text portions of this message have been removed]
      • paulkccd
        Greg, the problem is possibly caused by the reflections of bright light from your optics. You may want to try to lower the brightness of the lightbox to get
        Message 3 of 30 , Jun 10, 2002
          Greg, the problem is possibly caused by the reflections of bright
          light from your optics. You may want to try to lower the brightness
          of the lightbox to get the flat frame to expose for 10-20 seconds.

          Actually, I don't understand how one can take flat-frames with an AO-
          7 in the path. The AO-7 adjusts the image position based on guiding
          errors. Wouldn't that mean that the flat-frame can potentially fall
          on different pixel coordinates than the actual image depending on the
          mirror position? Seems to me that this would be similar to a serious
          mirror flop in an SCT...

          -Paul K
          http://pk.darkhorizons.org


          --- In ccd-newastro@y..., "Greg Crawford" <gc@n...> wrote:
          > Hi Everyone,
          >
          > I recently purchased Ron's book and thought I had better join the
          list.
          >
          > Can I kick off with a question about a flat-field problem I am
          having? I use
          > lightbox flats and lately have found that the image reduction in
          CCDSoftV5
          > leaves traces of a negative image of the flat-field on the light
          frame after
          > auto-reduction. You can see what I mean here:
          >
          > http://www.nelsonbay.com/~gc/Publication2.htm
          >
          > I have exposed the flat-fields for 2 seconds, which is enough to
          make the
          > maximum pixel value about 20,000, which is approximately one third
          of my maximum
          > of 65535 on an ST9E. The strange flat-field comes from having an AO-
          7 in the
          > optical train.
          >
          > Can anyone suggest what is causing the problem?
          >
          > Greg Crawford
          > Observing from Southern Skies
          >
          > *
          >
          > * *
          > *
          >
          >
          > *
          >
          > http://www.nelsonbay.com/~gc/observatory.htm
          >
          > "Though my soul may set in darkness, it will rise in perfect light,
          > I have loved the stars too dearly to be fearful of the night."
          > - from the gravestone of astronomer, John
          Brashear.
          >
          >
          >
          > ______________________________________
          > Scanned and protected by Inflex
          > http://pldaniels.com/inflex
        • John Smith
          Hi Greg, You may want to try some sky flats to see how well they agree with your light box, especially if you evaluate the flat field critically. I ve found
          Message 4 of 30 , Jun 10, 2002
            Hi Greg,

            You may want to try some sky flats to see how well they agree with your
            light box, especially if you evaluate the flat field critically. I've found
            that the most accurate flat is a sky flat and have seen light box flats
            leave the image you describe. It turns out that a foam light box, along the
            lines of what Gerry Melino did, is actually a bit better than a conventional
            light box, at least in my case. Here is a link to Gerry's design:
            http://www.melino.org/astronomy/light_box.html
            I modified the design by adding a second foam sheet in front to further
            diffuse the image. But I generally use sky flats and have been very
            satisfied with them.

            John
            http://www.hiddenloft.darkhorizons.org/

            -----Original Message-----
            From: Greg Crawford [mailto:gc@...]
            Sent: Monday, June 10, 2002 6:11 AM
            To: 'CCD NewAstro List'
            Subject: [ccd-newastro] Hi and Flat-Field Problem

            Hi Everyone,

            I recently purchased Ron's book and thought I had better join the list.

            Can I kick off with a question about a flat-field problem I am having? I use
            lightbox flats and lately have found that the image reduction in CCDSoftV5
            leaves traces of a negative image of the flat-field on the light frame after
            auto-reduction. You can see what I mean here:

            http://www.nelsonbay.com/~gc/Publication2.htm

            I have exposed the flat-fields for 2 seconds, which is enough to make the
            maximum pixel value about 20,000, which is approximately one third of my
            maximum
            of 65535 on an ST9E. The strange flat-field comes from having an AO-7 in the
            optical train.

            Can anyone suggest what is causing the problem?

            Greg Crawford
            Observing from Southern Skies

            *

            * *
            *


            *

            http://www.nelsonbay.com/~gc/observatory.htm

            "Though my soul may set in darkness, it will rise in perfect light,
            I have loved the stars too dearly to be fearful of the night."
            - from the gravestone of astronomer, John Brashear.



            ______________________________________
            Scanned and protected by Inflex
            http://pldaniels.com/inflex


            To unsubscribe from this group, send an email to:
            ccd-newastro-unsubscribe@egroups.com



            Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
          • randy_nulman
            Paul, The AO7 is still guide star dependent..actually more accurate. Therefore, I would think that it shouldn t affect flats at all. The final results of the
            Message 5 of 30 , Jun 10, 2002
              Paul,

              The AO7 is still "guide star" dependent..actually more accurate.
              Therefore, I would think that it shouldn't affect flats at all.
              The final results of the "light" image, using an AO7 should be very
              accurate (sub pixel error), so the flat should work just fine.

              Randy Nulman

              --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
              > Greg, the problem is possibly caused by the reflections of bright
              > light from your optics. You may want to try to lower the brightness
              > of the lightbox to get the flat frame to expose for 10-20 seconds.
              >
              > Actually, I don't understand how one can take flat-frames with an
              AO-
              > 7 in the path. The AO-7 adjusts the image position based on guiding
              > errors. Wouldn't that mean that the flat-frame can potentially fall
              > on different pixel coordinates than the actual image depending on
              the
              > mirror position? Seems to me that this would be similar to a
              serious
              > mirror flop in an SCT...
              >
              > -Paul K
              > http://pk.darkhorizons.org
              >
              >
              > --- In ccd-newastro@y..., "Greg Crawford" <gc@n...> wrote:
              > > Hi Everyone,
              > >
              > > I recently purchased Ron's book and thought I had better join the
              > list.
              > >
              > > Can I kick off with a question about a flat-field problem I am
              > having? I use
              > > lightbox flats and lately have found that the image reduction in
              > CCDSoftV5
              > > leaves traces of a negative image of the flat-field on the light
              > frame after
              > > auto-reduction. You can see what I mean here:
              > >
              > > http://www.nelsonbay.com/~gc/Publication2.htm
              > >
              > > I have exposed the flat-fields for 2 seconds, which is enough to
              > make the
              > > maximum pixel value about 20,000, which is approximately one
              third
              > of my maximum
              > > of 65535 on an ST9E. The strange flat-field comes from having an
              AO-
              > 7 in the
              > > optical train.
              > >
              > > Can anyone suggest what is causing the problem?
              > >
              > > Greg Crawford
              > > Observing from Southern Skies
              > >
              > > *
              > >
              > > * *
              > > *
              > >
              > >
              > > *
              > >
              > > http://www.nelsonbay.com/~gc/observatory.htm
              > >
              > > "Though my soul may set in darkness, it will rise in perfect
              light,
              > > I have loved the stars too dearly to be fearful of the night."
              > > - from the gravestone of astronomer, John
              > Brashear.
              > >
              > >
              > >
              > > ______________________________________
              > > Scanned and protected by Inflex
              > > http://pldaniels.com/inflex
            • Ron Wodaski
              The AO-7 operates by bending the optical path, while the vignetting remains stationary. This _might_ result in funky flats on some setups; only testing will
              Message 6 of 30 , Jun 10, 2002
                The AO-7 operates by bending the optical path, while the vignetting remains
                stationary. This _might_ result in funky flats on some setups; only testing
                will tell. I'm going to comment separately about Greg's sample flat
                application.

                Ron Wodaski
                author of The New CCD Astronomy
                http://www.newastro.com


                -----Original Message-----
                From: randy_nulman [mailto:rjnulman@...]
                Sent: Monday, June 10, 2002 12:54 PM
                To: ccd-newastro@yahoogroups.com
                Subject: [ccd-newastro] Re: Hi and Flat-Field Problem


                Paul,

                The AO7 is still "guide star" dependent..actually more accurate.
                Therefore, I would think that it shouldn't affect flats at all.
                The final results of the "light" image, using an AO7 should be very
                accurate (sub pixel error), so the flat should work just fine.

                Randy Nulman

                --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                > Greg, the problem is possibly caused by the reflections of bright
                > light from your optics. You may want to try to lower the brightness
                > of the lightbox to get the flat frame to expose for 10-20 seconds.
                >
                > Actually, I don't understand how one can take flat-frames with an
                AO-
                > 7 in the path. The AO-7 adjusts the image position based on guiding
                > errors. Wouldn't that mean that the flat-frame can potentially fall
                > on different pixel coordinates than the actual image depending on
                the
                > mirror position? Seems to me that this would be similar to a
                serious
                > mirror flop in an SCT...
                >
                > -Paul K
                > http://pk.darkhorizons.org
                >
                >
                > --- In ccd-newastro@y..., "Greg Crawford" <gc@n...> wrote:
                > > Hi Everyone,
                > >
                > > I recently purchased Ron's book and thought I had better join the
                > list.
                > >
                > > Can I kick off with a question about a flat-field problem I am
                > having? I use
                > > lightbox flats and lately have found that the image reduction in
                > CCDSoftV5
                > > leaves traces of a negative image of the flat-field on the light
                > frame after
                > > auto-reduction. You can see what I mean here:
                > >
                > > http://www.nelsonbay.com/~gc/Publication2.htm
                > >
                > > I have exposed the flat-fields for 2 seconds, which is enough to
                > make the
                > > maximum pixel value about 20,000, which is approximately one
                third
                > of my maximum
                > > of 65535 on an ST9E. The strange flat-field comes from having an
                AO-
                > 7 in the
                > > optical train.
                > >
                > > Can anyone suggest what is causing the problem?
                > >
                > > Greg Crawford
                > > Observing from Southern Skies
                > >
                > > *
                > >
                > > * *
                > > *
                > >
                > >
                > > *
                > >
                > > http://www.nelsonbay.com/~gc/observatory.htm
                > >
                > > "Though my soul may set in darkness, it will rise in perfect
                light,
                > > I have loved the stars too dearly to be fearful of the night."
                > > - from the gravestone of astronomer, John
                > Brashear.
                > >
                > >
                > >
                > > ______________________________________
                > > Scanned and protected by Inflex
                > > http://pldaniels.com/inflex



                To unsubscribe from this group, send an email to:
                ccd-newastro-unsubscribe@egroups.com



                Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
              • paulkccd
                I guess it all depends on the amount of correction provided by the AO- 7. If it s within 1/2 a pixel, the flat is likely to be accurate enough. Any errors
                Message 7 of 30 , Jun 10, 2002
                  I guess it all depends on the amount of correction provided by the AO-
                  7. If it's within 1/2 a pixel, the flat is likely to be accurate
                  enough. Any errors greater than that and the flat may be offset by a
                  pixel or more.

                  According to SBIG the AO-7 can provide as much as 50 pixels
                  correction at 2000mm focal length with an ST-7 pixel size. Any flat
                  frame shifted by this much will be badly offset from where it should
                  be. Am I missing something?

                  -Paul K

                  --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                  > Paul,
                  >
                  > The AO7 is still "guide star" dependent..actually more accurate.
                  > Therefore, I would think that it shouldn't affect flats at all.
                  > The final results of the "light" image, using an AO7 should be very
                  > accurate (sub pixel error), so the flat should work just fine.
                  >
                  > Randy Nulman
                  >
                  > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                  > > Greg, the problem is possibly caused by the reflections of bright
                  > > light from your optics. You may want to try to lower the
                  brightness
                  > > of the lightbox to get the flat frame to expose for 10-20 seconds.
                  > >
                  > > Actually, I don't understand how one can take flat-frames with an
                  > AO-
                  > > 7 in the path. The AO-7 adjusts the image position based on
                  guiding
                  > > errors. Wouldn't that mean that the flat-frame can potentially
                  fall
                  > > on different pixel coordinates than the actual image depending on
                  > the
                  > > mirror position? Seems to me that this would be similar to a
                  > serious
                  > > mirror flop in an SCT...
                  > >
                  > > -Paul K
                  > > http://pk.darkhorizons.org
                  > >
                • randy_nulman
                  Ron, Thanks for correcting me. I understood Paul s comments, but I thought the amount of bending from the AO7 was so _minimal_ that the net result (in
                  Message 8 of 30 , Jun 10, 2002
                    Ron,
                    Thanks for correcting me. I understood Paul's comments, but I
                    thought the amount of "bending" from the AO7 was so _minimal_ that
                    the net result (in relation to the flat, vignetting, etc.) was
                    minimal at best?

                    Having just received an AO7, how does one go about the "testing"
                    routine? My "lightbox" flats worked well for "standard" guiding.

                    Thanks,
                    Randy

                    --- In ccd-newastro@y..., "Ron Wodaski" <ronw@p...> wrote:
                    > The AO-7 operates by bending the optical path, while the vignetting
                    remains
                    > stationary. This _might_ result in funky flats on some setups; only
                    testing
                    > will tell. I'm going to comment separately about Greg's sample flat
                    > application.
                    >
                    > Ron Wodaski
                    > author of The New CCD Astronomy
                    > http://www.newastro.com
                    >
                    >
                    > -----Original Message-----
                    > From: randy_nulman [mailto:rjnulman@w...]
                    > Sent: Monday, June 10, 2002 12:54 PM
                    > To: ccd-newastro@y...
                    > Subject: [ccd-newastro] Re: Hi and Flat-Field Problem
                    >
                    >
                    > Paul,
                    >
                    > The AO7 is still "guide star" dependent..actually more accurate.
                    > Therefore, I would think that it shouldn't affect flats at all.
                    > The final results of the "light" image, using an AO7 should be very
                    > accurate (sub pixel error), so the flat should work just fine.
                    >
                    > Randy Nulman
                    >
                    > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                    > > Greg, the problem is possibly caused by the reflections of bright
                    > > light from your optics. You may want to try to lower the
                    brightness
                    > > of the lightbox to get the flat frame to expose for 10-20 seconds.
                    > >
                    > > Actually, I don't understand how one can take flat-frames with an
                    > AO-
                    > > 7 in the path. The AO-7 adjusts the image position based on
                    guiding
                    > > errors. Wouldn't that mean that the flat-frame can potentially
                    fall
                    > > on different pixel coordinates than the actual image depending on
                    > the
                    > > mirror position? Seems to me that this would be similar to a
                    > serious
                    > > mirror flop in an SCT...
                    > >
                    > > -Paul K
                    > > http://pk.darkhorizons.org
                    > >
                    > >
                    > > --- In ccd-newastro@y..., "Greg Crawford" <gc@n...> wrote:
                    > > > Hi Everyone,
                    > > >
                    > > > I recently purchased Ron's book and thought I had better join
                    the
                    > > list.
                    > > >
                    > > > Can I kick off with a question about a flat-field problem I am
                    > > having? I use
                    > > > lightbox flats and lately have found that the image reduction in
                    > > CCDSoftV5
                    > > > leaves traces of a negative image of the flat-field on the light
                    > > frame after
                    > > > auto-reduction. You can see what I mean here:
                    > > >
                    > > > http://www.nelsonbay.com/~gc/Publication2.htm
                    > > >
                    > > > I have exposed the flat-fields for 2 seconds, which is enough to
                    > > make the
                    > > > maximum pixel value about 20,000, which is approximately one
                    > third
                    > > of my maximum
                    > > > of 65535 on an ST9E. The strange flat-field comes from having an
                    > AO-
                    > > 7 in the
                    > > > optical train.
                    > > >
                    > > > Can anyone suggest what is causing the problem?
                    > > >
                    > > > Greg Crawford
                    > > > Observing from Southern Skies
                    > > >
                    > > > *
                    > > >
                    > > > * *
                    > > > *
                    > > >
                    > > >
                    > > > *
                    > > >
                    > > > http://www.nelsonbay.com/~gc/observatory.htm
                    > > >
                    > > > "Though my soul may set in darkness, it will rise in perfect
                    > light,
                    > > > I have loved the stars too dearly to be fearful of the night."
                    > > > - from the gravestone of astronomer, John
                    > > Brashear.
                    > > >
                    > > >
                    > > >
                    > > > ______________________________________
                    > > > Scanned and protected by Inflex
                    > > > http://pldaniels.com/inflex
                    >
                    >
                    >
                    > To unsubscribe from this group, send an email to:
                    > ccd-newastro-unsubscribe@e...
                    >
                    >
                    >
                    > Your use of Yahoo! Groups is subject to
                    http://docs.yahoo.com/info/terms/
                  • randy_nulman
                    See Ron s post regarding my answer to your first post. Seems I m making assumptions about the amount of AO7 corrections that are not correct! Based on the info
                    Message 9 of 30 , Jun 10, 2002
                      See Ron's post regarding my answer to your first post.
                      Seems I'm making assumptions about the amount of AO7 corrections that
                      are not correct!

                      Based on the info you just gave, I can fully see your point.

                      Randy

                      --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                      > I guess it all depends on the amount of correction provided by the
                      AO-
                      > 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                      > enough. Any errors greater than that and the flat may be offset by
                      a
                      > pixel or more.
                      >
                      > According to SBIG the AO-7 can provide as much as 50 pixels
                      > correction at 2000mm focal length with an ST-7 pixel size. Any flat
                      > frame shifted by this much will be badly offset from where it
                      should
                      > be. Am I missing something?
                      >
                      > -Paul K
                      >
                      > --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                      > > Paul,
                      > >
                      > > The AO7 is still "guide star" dependent..actually more accurate.
                      > > Therefore, I would think that it shouldn't affect flats at all.
                      > > The final results of the "light" image, using an AO7 should be
                      very
                      > > accurate (sub pixel error), so the flat should work just fine.
                      > >
                      > > Randy Nulman
                      > >
                      > > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                      > > > Greg, the problem is possibly caused by the reflections of
                      bright
                      > > > light from your optics. You may want to try to lower the
                      > brightness
                      > > > of the lightbox to get the flat frame to expose for 10-20
                      seconds.
                      > > >
                      > > > Actually, I don't understand how one can take flat-frames with
                      an
                      > > AO-
                      > > > 7 in the path. The AO-7 adjusts the image position based on
                      > guiding
                      > > > errors. Wouldn't that mean that the flat-frame can potentially
                      > fall
                      > > > on different pixel coordinates than the actual image depending
                      on
                      > > the
                      > > > mirror position? Seems to me that this would be similar to a
                      > > serious
                      > > > mirror flop in an SCT...
                      > > >
                      > > > -Paul K
                      > > > http://pk.darkhorizons.org
                      > > >
                    • Greg Crawford
                      Thanks to all for suggestions so far. Chris, I re-did the reductions in AIP4WIN and got the same problematic result as in CCDSoftV5. So I won t send any files
                      Message 10 of 30 , Jun 10, 2002
                        Thanks to all for suggestions so far.

                        Chris, I re-did the reductions in AIP4WIN and got the same problematic result as
                        in CCDSoftV5. So I won't send any files (thanks for your offer, all the same.)

                        Paul, following your suggestion, I dropped the voltage on the lightbox and did
                        15 second flat-field frames, but alas, no difference. However, the reflections
                        idea might bear more following up.

                        John, I used to use twilight flats, but found I had a gradient in them. Also, I
                        like to do 16 frames for each flat and median combine for lower noise, and
                        there's not much of a "window of opportunity" for twilight flats, especially if
                        you want them in clear, B, V, R & I.

                        As for the AO-7 complicating flats ... I wonder?

                        Greg Crawford
                        Observing from Southern Skies

                        *

                        * *
                        *


                        *

                        http://www.nelsonbay.com/~gc/observatory.htm

                        "Though my soul may set in darkness, it will rise in perfect light,
                        I have loved the stars too dearly to be fearful of the night."
                        - from the gravestone of astronomer, John Brashear.




                        ______________________________________
                        Scanned and protected by Inflex
                        http://pldaniels.com/inflex
                      • Ron Wodaski
                        Greg, here s my thinking on your flat. The usual cause of trouble with flats is that they aren t in fact flat -- uneven illumination is the bade of the
                        Message 11 of 30 , Jun 10, 2002
                          Greg, here's my thinking on your flat. The usual cause of trouble with flats
                          is that they aren't in fact flat -- uneven illumination is the bade of the
                          imager's existence. Light boxes are helpful, but they, like T-shirt flats
                          and anything else besides a good sky flat, are difficult to illuminate
                          evenly. In addition, you can wind up illuminating things inside the scope
                          that aren't normally subject to much light, resulting in an unbalanced flat.

                          These differences are often subtle - but if you have a lot of light
                          pollution, bright moonlight, or strong nearby light sources, there is enough
                          light bouncing around that even a slight mis-match will show up in your
                          images.

                          Worst-case problems of this sort include:

                          * Light entering through the back end of the scope and illuminating things
                          that should be in shadow (common with daylight flats, and a problem if there
                          is the slightest light leak at the back of the scope).

                          * Materials that shift light preferentially. This includes quasi-crystalline
                          effects that reflect light internally, creating bright spots where there
                          would be none in normal imaging; inadequate diffusion; illumination of
                          interior surfaces that cause reflections that lead to hot spots, secondary
                          illumination of surfaces in the optical path; etc.

                          * Good old fashioned failure to illuminate evenly from your primary source.

                          If you run into these problems, your best bet is to take 25-50 images of the
                          sky on a night with at least high clouds to create a strong sky brightness.
                          I have been able to make good flats out of 3-minute exposures randomly
                          placed on the sky. But you need a fairly bright sky to pull that off. Clouds
                          are better. Even thin high clouds will work; if you have enough images, a
                          median combine will clean out the stars amazingly well. If you wind up with
                          single stars that are very bright, you can omit them from the combine, or
                          clean them up with Edit Pixels afterwards.

                          A good sky flat can be a pain to take, and many times simpler methods of
                          making flats will do well enough. But for times when alternatives won't do
                          good enough, sky flats are the best solution. A sky flat taken at the same
                          approximate position as the light frames can even compensate to some degree
                          for light pollution gradients.

                          The residual brightness I see in your posted image is low enough that it can
                          probably be cleaned up really well with an artificial flat built in
                          Photoshop by manually removing the stars from the image (Dust & Scratches
                          filter and/or cloning). That might ultimately be simpler than taking good
                          sky flats, but if you need to closely calibrate for photometry, I would
                          recommend getting a good set of sky flats in hand.

                          Ron Wodaski
                          author of The New CCD Astronomy
                          http://www.newastro.com


                          -----Original Message-----
                          From: Greg Crawford [mailto:gc@...]
                          Sent: Monday, June 10, 2002 5:05 PM
                          To: ccd-newastro@yahoogroups.com
                          Subject: RE: [ccd-newastro] Re: Hi and Flat-Field Problem


                          Thanks to all for suggestions so far.

                          Chris, I re-did the reductions in AIP4WIN and got the same problematic
                          result as
                          in CCDSoftV5. So I won't send any files (thanks for your offer, all the
                          same.)

                          Paul, following your suggestion, I dropped the voltage on the lightbox and
                          did
                          15 second flat-field frames, but alas, no difference. However, the
                          reflections
                          idea might bear more following up.

                          John, I used to use twilight flats, but found I had a gradient in them.
                          Also, I
                          like to do 16 frames for each flat and median combine for lower noise, and
                          there's not much of a "window of opportunity" for twilight flats, especially
                          if
                          you want them in clear, B, V, R & I.

                          As for the AO-7 complicating flats ... I wonder?

                          Greg Crawford
                          Observing from Southern Skies

                          *

                          * *
                          *


                          *

                          http://www.nelsonbay.com/~gc/observatory.htm

                          "Though my soul may set in darkness, it will rise in perfect light,
                          I have loved the stars too dearly to be fearful of the night."
                          - from the gravestone of astronomer, John Brashear.




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                        • Greg Crawford
                          Ron, Thanks for these suggestions. The problem with night sky flats is that they require many images, and, like other flats, need to be done each time the
                          Message 12 of 30 , Jun 10, 2002
                            Ron,

                            Thanks for these suggestions. The problem with night sky flats is that they
                            require many images, and, like other flats, need to be done each time the
                            camera is removed from the scope and then replaced. For security reasons, I do
                            this every night.

                            I will follow up your suggestions about internal reflections. To begin with, I
                            will try removing the JMI focuser from the optical train. I have my eyes on a
                            TCF-S, but I'm not sure whether that would solve anything if the focuser is the
                            cause.

                            - Greg

                            >-----Original Message-----
                            >From: Ron Wodaski [mailto:ronw@...]
                            >Sent: Tuesday, 11 June 2002 10:53 AM
                            >To: ccd-newastro@yahoogroups.com
                            >Subject: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                            >
                            >
                            >Greg, here's my thinking on your flat. The usual cause of
                            >trouble with flats
                            >is that they aren't in fact flat -- uneven illumination is the
                            >bade of the
                            >imager's existence. Light boxes are helpful, but they, like
                            >T-shirt flats
                            >and anything else besides a good sky flat, are difficult to illuminate
                            >evenly. In addition, you can wind up illuminating things
                            >inside the scope
                            >that aren't normally subject to much light, resulting in an
                            >unbalanced flat.
                            >
                            >These differences are often subtle - but if you have a lot of light
                            >pollution, bright moonlight, or strong nearby light sources,
                            >there is enough
                            >light bouncing around that even a slight mis-match will show up in your
                            >images.
                            >
                            >Worst-case problems of this sort include:
                            >
                            >* Light entering through the back end of the scope and
                            >illuminating things
                            >that should be in shadow (common with daylight flats, and a
                            >problem if there
                            >is the slightest light leak at the back of the scope).
                            >
                            >* Materials that shift light preferentially. This includes
                            >quasi-crystalline
                            >effects that reflect light internally, creating bright spots
                            >where there
                            >would be none in normal imaging; inadequate diffusion; illumination of
                            >interior surfaces that cause reflections that lead to hot
                            >spots, secondary
                            >illumination of surfaces in the optical path; etc.
                            >
                            >* Good old fashioned failure to illuminate evenly from your
                            >primary source.
                            >
                            >If you run into these problems, your best bet is to take 25-50
                            >images of the
                            >sky on a night with at least high clouds to create a strong
                            >sky brightness.
                            >I have been able to make good flats out of 3-minute exposures randomly
                            >placed on the sky. But you need a fairly bright sky to pull
                            >that off. Clouds
                            >are better. Even thin high clouds will work; if you have
                            >enough images, a
                            >median combine will clean out the stars amazingly well. If you
                            >wind up with
                            >single stars that are very bright, you can omit them from the
                            >combine, or
                            >clean them up with Edit Pixels afterwards.
                            >
                            >A good sky flat can be a pain to take, and many times simpler
                            >methods of
                            >making flats will do well enough. But for times when
                            >alternatives won't do
                            >good enough, sky flats are the best solution. A sky flat taken
                            >at the same
                            >approximate position as the light frames can even compensate
                            >to some degree
                            >for light pollution gradients.
                            >
                            >The residual brightness I see in your posted image is low
                            >enough that it can
                            >probably be cleaned up really well with an artificial flat built in
                            >Photoshop by manually removing the stars from the image (Dust
                            >& Scratches
                            >filter and/or cloning). That might ultimately be simpler than
                            >taking good
                            >sky flats, but if you need to closely calibrate for photometry, I would
                            >recommend getting a good set of sky flats in hand.
                            >
                            >Ron Wodaski
                            >author of The New CCD Astronomy
                            >http://www.newastro.com
                            >
                            >
                            >-----Original Message-----
                            >From: Greg Crawford [mailto:gc@...]
                            >Sent: Monday, June 10, 2002 5:05 PM
                            >To: ccd-newastro@yahoogroups.com
                            >Subject: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                            >
                            >
                            >Thanks to all for suggestions so far.
                            >
                            >Chris, I re-did the reductions in AIP4WIN and got the same problematic
                            >result as
                            >in CCDSoftV5. So I won't send any files (thanks for your offer, all the
                            >same.)
                            >
                            >Paul, following your suggestion, I dropped the voltage on the
                            >lightbox and
                            >did
                            >15 second flat-field frames, but alas, no difference. However, the
                            >reflections
                            >idea might bear more following up.
                            >
                            >John, I used to use twilight flats, but found I had a gradient in them.
                            >Also, I
                            >like to do 16 frames for each flat and median combine for
                            >lower noise, and
                            >there's not much of a "window of opportunity" for twilight
                            >flats, especially
                            >if
                            >you want them in clear, B, V, R & I.
                            >
                            >As for the AO-7 complicating flats ... I wonder?
                            >
                            >Greg Crawford
                            >Observing from Southern Skies
                            >
                            > *
                            >
                            > * *
                            > *
                            >
                            >
                            > *
                            >
                            >http://www.nelsonbay.com/~gc/observatory.htm
                            >
                            >"Though my soul may set in darkness, it will rise in perfect light,
                            > I have loved the stars too dearly to be fearful of the night."
                            > - from the gravestone of astronomer,
                            >John Brashear.
                            >
                            >
                            >
                            >
                            >______________________________________
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                            >
                            >
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                          • morrinho@t-online.de
                            May I ask you something what is perhaps a stupid question so please excuse this as well as my bad English. You are not talking about taking a flat with the AO7
                            Message 13 of 30 , Jun 11, 2002
                              May I ask you something what is perhaps a stupid question so please
                              excuse this as well as my bad English.

                              You are not talking about taking a flat with the AO7 running, are you.
                              And having the AO7 mirror switched off, does it not come into sero position?
                              Or is it just that what you are talking about?

                              Rolf

                              > -----Ursprüngliche Nachricht-----
                              > Von: paulkccd [mailto:pkane2001@...]
                              > Gesendet: Montag, 10. Juni 2002 22:51
                              > An: ccd-newastro@yahoogroups.com
                              > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                              >
                              >
                              > I guess it all depends on the amount of correction provided by the AO-
                              > 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                              > enough. Any errors greater than that and the flat may be offset by a
                              > pixel or more.
                              >
                              > According to SBIG the AO-7 can provide as much as 50 pixels
                              > correction at 2000mm focal length with an ST-7 pixel size. Any flat
                              > frame shifted by this much will be badly offset from where it should
                              > be. Am I missing something?
                              >
                              > -Paul K
                              >
                              > --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                              > > Paul,
                              > >
                              > > The AO7 is still "guide star" dependent..actually more accurate.
                              > > Therefore, I would think that it shouldn't affect flats at all.
                              > > The final results of the "light" image, using an AO7 should be very
                              > > accurate (sub pixel error), so the flat should work just fine.
                              > >
                              > > Randy Nulman
                              > >
                              > > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                              > > > Greg, the problem is possibly caused by the reflections of bright
                              > > > light from your optics. You may want to try to lower the
                              > brightness
                              > > > of the lightbox to get the flat frame to expose for 10-20 seconds.
                              > > >
                              > > > Actually, I don't understand how one can take flat-frames with an
                              > > AO-
                              > > > 7 in the path. The AO-7 adjusts the image position based on
                              > guiding
                              > > > errors. Wouldn't that mean that the flat-frame can potentially
                              > fall
                              > > > on different pixel coordinates than the actual image depending on
                              > > the
                              > > > mirror position? Seems to me that this would be similar to a
                              > > serious
                              > > > mirror flop in an SCT...
                              > > >
                              > > > -Paul K
                              > > > http://pk.darkhorizons.org
                              > > >
                              >
                              >
                              >
                              >
                              > To unsubscribe from this group, send an email to:
                              > ccd-newastro-unsubscribe@egroups.com
                              >
                              >
                              >
                              > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                              >
                              >
                            • Greg Crawford
                              Hi Rolf, When you say with the AO-7 running, I am not sure what you mean. I am using CCDSoftV5 AO-7 pre-release. You connect to the camera with the AO-7
                              Message 14 of 30 , Jun 11, 2002
                                Hi Rolf,

                                When you say with the AO-7 running, I am not sure what you mean. I am using
                                CCDSoftV5 AO-7 pre-release. You connect to the camera with the AO-7 physically
                                connected to the camera. Flat-fields are taken, with the "AO Enabled" box
                                checked, but not guiding.

                                - Greg

                                >-----Original Message-----
                                >From: morrinho@... [mailto:morrinho@...]
                                >Sent: Wednesday, 12 June 2002 12:45 AM
                                >To: ccd-newastro@yahoogroups.com
                                >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                >
                                >
                                >May I ask you something what is perhaps a stupid question so please
                                >excuse this as well as my bad English.
                                >
                                > You are not talking about taking a flat with the AO7
                                >running, are you.
                                >And having the AO7 mirror switched off, does it not come into
                                >sero position?
                                >Or is it just that what you are talking about?
                                >
                                >Rolf
                                >
                                >> -----Ursprüngliche Nachricht-----
                                >> Von: paulkccd [mailto:pkane2001@...]
                                >> Gesendet: Montag, 10. Juni 2002 22:51
                                >> An: ccd-newastro@yahoogroups.com
                                >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                >>
                                >>
                                >> I guess it all depends on the amount of correction provided
                                >by the AO-
                                >> 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                >> enough. Any errors greater than that and the flat may be offset by a
                                >> pixel or more.
                                >>
                                >> According to SBIG the AO-7 can provide as much as 50 pixels
                                >> correction at 2000mm focal length with an ST-7 pixel size. Any flat
                                >> frame shifted by this much will be badly offset from where it should
                                >> be. Am I missing something?
                                >>
                                >> -Paul K
                                >>
                                >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                >> > Paul,
                                >> >
                                >> > The AO7 is still "guide star" dependent..actually more accurate.
                                >> > Therefore, I would think that it shouldn't affect flats at all.
                                >> > The final results of the "light" image, using an AO7 should be very
                                >> > accurate (sub pixel error), so the flat should work just fine.
                                >> >
                                >> > Randy Nulman
                                >> >
                                >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                >> > > Greg, the problem is possibly caused by the reflections of bright
                                >> > > light from your optics. You may want to try to lower the
                                >> brightness
                                >> > > of the lightbox to get the flat frame to expose for
                                >10-20 seconds.
                                >> > >
                                >> > > Actually, I don't understand how one can take flat-frames with an
                                >> > AO-
                                >> > > 7 in the path. The AO-7 adjusts the image position based on
                                >> guiding
                                >> > > errors. Wouldn't that mean that the flat-frame can potentially
                                >> fall
                                >> > > on different pixel coordinates than the actual image depending on
                                >> > the
                                >> > > mirror position? Seems to me that this would be similar to a
                                >> > serious
                                >> > > mirror flop in an SCT...
                                >> > >
                                >> > > -Paul K
                                >> > > http://pk.darkhorizons.org
                                >> > >
                                >>
                                >>
                                >>
                                >>
                                >> To unsubscribe from this group, send an email to:
                                >> ccd-newastro-unsubscribe@egroups.com
                                >>
                                >>
                                >>
                                >> Your use of Yahoo! Groups is subject to
                                >http://docs.yahoo.com/info/terms/
                                >>
                                >>
                                >
                                >
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                              • paulkccd
                                I assume that the AO-7 will come to some home or zero position when not guiding, but that doesn t solve the problem. Consider what happens when the AO-7 is
                                Message 15 of 30 , Jun 11, 2002
                                  I assume that the AO-7 will come to some "home" or zero position when
                                  not guiding, but that doesn't solve the problem.

                                  Consider what happens when the AO-7 is guiding. Say the tracking
                                  error in the mount is such that a correction of 10 pixels is
                                  required. The AO-7 bends the light so as to compensate for the error.
                                  The result is that now the center of the flat frame has shifted by 10
                                  pixels from its original location. As AO-7 guides, any correction
                                  will shift the center of the flat frame by that amount. At the end of
                                  the exposure, the flat frame will be averaged in to the final image
                                  at all the shift positions that the AO-7 had to visit while guiding.

                                  As I see it, the way to work around this is to use the
                                  mount "bumping" for any errors over 1 pixel, while using the AO-7 to
                                  guide out the errors that are less than 1 pixel in size.

                                  -Paul K
                                  http://pk.darkhorizons.org


                                  --- In ccd-newastro@y..., morrinho@t... wrote:
                                  > May I ask you something what is perhaps a stupid question so please
                                  > excuse this as well as my bad English.
                                  >
                                  > You are not talking about taking a flat with the AO7 running,
                                  are you.
                                  > And having the AO7 mirror switched off, does it not come into sero
                                  position?
                                  > Or is it just that what you are talking about?
                                  >
                                  > Rolf
                                  >
                                  > > -----Ursprüngliche Nachricht-----
                                  > > Von: paulkccd [mailto:pkane2001@h...]
                                  > > Gesendet: Montag, 10. Juni 2002 22:51
                                  > > An: ccd-newastro@y...
                                  > > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                  > >
                                  > >
                                  > > I guess it all depends on the amount of correction provided by
                                  the AO-
                                  > > 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                  > > enough. Any errors greater than that and the flat may be offset
                                  by a
                                  > > pixel or more.
                                  > >
                                  > > According to SBIG the AO-7 can provide as much as 50 pixels
                                  > > correction at 2000mm focal length with an ST-7 pixel size. Any
                                  flat
                                  > > frame shifted by this much will be badly offset from where it
                                  should
                                  > > be. Am I missing something?
                                  > >
                                  > > -Paul K
                                  > >
                                  > > --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                  > > > Paul,
                                  > > >
                                  > > > The AO7 is still "guide star" dependent..actually more accurate.
                                  > > > Therefore, I would think that it shouldn't affect flats at all.
                                  > > > The final results of the "light" image, using an AO7 should be
                                  very
                                  > > > accurate (sub pixel error), so the flat should work just fine.
                                  > > >
                                  > > > Randy Nulman
                                  > > >
                                  > > > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                  > > > > Greg, the problem is possibly caused by the reflections of
                                  bright
                                  > > > > light from your optics. You may want to try to lower the
                                  > > brightness
                                  > > > > of the lightbox to get the flat frame to expose for 10-20
                                  seconds.
                                  > > > >
                                  > > > > Actually, I don't understand how one can take flat-frames
                                  with an
                                  > > > AO-
                                  > > > > 7 in the path. The AO-7 adjusts the image position based on
                                  > > guiding
                                  > > > > errors. Wouldn't that mean that the flat-frame can potentially
                                  > > fall
                                  > > > > on different pixel coordinates than the actual image
                                  depending on
                                  > > > the
                                  > > > > mirror position? Seems to me that this would be similar to a
                                  > > > serious
                                  > > > > mirror flop in an SCT...
                                  > > > >
                                  > > > > -Paul K
                                  > > > > http://pk.darkhorizons.org
                                  > > > >
                                  > >
                                  > >
                                  > >
                                  > >
                                  > > To unsubscribe from this group, send an email to:
                                  > > ccd-newastro-unsubscribe@e...
                                  > >
                                  > >
                                  > >
                                  > > Your use of Yahoo! Groups is subject to
                                  http://docs.yahoo.com/info/terms/
                                  > >
                                  > >
                                • Ron Wodaski
                                  You might also be able to solve the practical issues by simply blurring the flat. This could be done so as to approximate the blurring in the virtual flat
                                  Message 16 of 30 , Jun 11, 2002
                                    You might also be able to solve the practical issues by simply blurring the
                                    flat. This could be done so as to approximate the blurring in the virtual
                                    flat induced by the AO-7. Might or might not work, but worth a try, I think.

                                    Ron Wodaski
                                    author of The New CCD Astronomy
                                    http://www.newastro.com


                                    -----Original Message-----
                                    From: paulkccd [mailto:pkane2001@...]
                                    Sent: Tuesday, June 11, 2002 9:27 AM
                                    To: ccd-newastro@yahoogroups.com
                                    Subject: [ccd-newastro] Re: Hi and Flat-Field Problem


                                    I assume that the AO-7 will come to some "home" or zero position when
                                    not guiding, but that doesn't solve the problem.

                                    Consider what happens when the AO-7 is guiding. Say the tracking
                                    error in the mount is such that a correction of 10 pixels is
                                    required. The AO-7 bends the light so as to compensate for the error.
                                    The result is that now the center of the flat frame has shifted by 10
                                    pixels from its original location. As AO-7 guides, any correction
                                    will shift the center of the flat frame by that amount. At the end of
                                    the exposure, the flat frame will be averaged in to the final image
                                    at all the shift positions that the AO-7 had to visit while guiding.

                                    As I see it, the way to work around this is to use the
                                    mount "bumping" for any errors over 1 pixel, while using the AO-7 to
                                    guide out the errors that are less than 1 pixel in size.

                                    -Paul K
                                    http://pk.darkhorizons.org


                                    --- In ccd-newastro@y..., morrinho@t... wrote:
                                    > May I ask you something what is perhaps a stupid question so please
                                    > excuse this as well as my bad English.
                                    >
                                    > You are not talking about taking a flat with the AO7 running,
                                    are you.
                                    > And having the AO7 mirror switched off, does it not come into sero
                                    position?
                                    > Or is it just that what you are talking about?
                                    >
                                    > Rolf
                                    >
                                    > > -----Ursprüngliche Nachricht-----
                                    > > Von: paulkccd [mailto:pkane2001@h...]
                                    > > Gesendet: Montag, 10. Juni 2002 22:51
                                    > > An: ccd-newastro@y...
                                    > > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                    > >
                                    > >
                                    > > I guess it all depends on the amount of correction provided by
                                    the AO-
                                    > > 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                    > > enough. Any errors greater than that and the flat may be offset
                                    by a
                                    > > pixel or more.
                                    > >
                                    > > According to SBIG the AO-7 can provide as much as 50 pixels
                                    > > correction at 2000mm focal length with an ST-7 pixel size. Any
                                    flat
                                    > > frame shifted by this much will be badly offset from where it
                                    should
                                    > > be. Am I missing something?
                                    > >
                                    > > -Paul K
                                    > >
                                    > > --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                    > > > Paul,
                                    > > >
                                    > > > The AO7 is still "guide star" dependent..actually more accurate.
                                    > > > Therefore, I would think that it shouldn't affect flats at all.
                                    > > > The final results of the "light" image, using an AO7 should be
                                    very
                                    > > > accurate (sub pixel error), so the flat should work just fine.
                                    > > >
                                    > > > Randy Nulman
                                    > > >
                                    > > > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                    > > > > Greg, the problem is possibly caused by the reflections of
                                    bright
                                    > > > > light from your optics. You may want to try to lower the
                                    > > brightness
                                    > > > > of the lightbox to get the flat frame to expose for 10-20
                                    seconds.
                                    > > > >
                                    > > > > Actually, I don't understand how one can take flat-frames
                                    with an
                                    > > > AO-
                                    > > > > 7 in the path. The AO-7 adjusts the image position based on
                                    > > guiding
                                    > > > > errors. Wouldn't that mean that the flat-frame can potentially
                                    > > fall
                                    > > > > on different pixel coordinates than the actual image
                                    depending on
                                    > > > the
                                    > > > > mirror position? Seems to me that this would be similar to a
                                    > > > serious
                                    > > > > mirror flop in an SCT...
                                    > > > >
                                    > > > > -Paul K
                                    > > > > http://pk.darkhorizons.org
                                    > > > >
                                    > >
                                    > >
                                    > >
                                    > >
                                    > > To unsubscribe from this group, send an email to:
                                    > > ccd-newastro-unsubscribe@e...
                                    > >
                                    > >
                                    > >
                                    > > Your use of Yahoo! Groups is subject to
                                    http://docs.yahoo.com/info/terms/
                                    > >
                                    > >



                                    To unsubscribe from this group, send an email to:
                                    ccd-newastro-unsubscribe@egroups.com



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                                  • morrinho@t-online.de
                                    Yes Greg, that is also the software I use and the way I use my AO7 for flats. But with the AO Enabled box checked, but not guiding.
                                    Message 17 of 30 , Jun 11, 2002
                                      Yes Greg, that is also the software I use and the way I use my AO7 for
                                      flats. But >with the "AO Enabled" box checked, but not guiding.< the
                                      AO7 is switched off, isn't it?

                                      I think what I missed up to now is that Paul doubted that the flat
                                      matches the light which was taken with a "swinging mirror" is that correct?

                                      Rolf

                                      > -----Ursprüngliche Nachricht-----
                                      > Von: Greg Crawford [mailto:gc@...]
                                      > Gesendet: Dienstag, 11. Juni 2002 17:20
                                      > An: ccd-newastro@yahoogroups.com
                                      > Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                      >
                                      >
                                      > Hi Rolf,
                                      >
                                      > When you say with the AO-7 running, I am not sure what you mean.
                                      > I am using
                                      > CCDSoftV5 AO-7 pre-release. You connect to the camera with the
                                      > AO-7 physically
                                      > connected to the camera. Flat-fields are taken, with the "AO Enabled" box
                                      > checked, but not guiding.
                                      >
                                      > - Greg
                                      >
                                      > >-----Original Message-----
                                      > >From: morrinho@... [mailto:morrinho@...]
                                      > >Sent: Wednesday, 12 June 2002 12:45 AM
                                      > >To: ccd-newastro@yahoogroups.com
                                      > >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                      > >
                                      > >
                                      > >May I ask you something what is perhaps a stupid question so please
                                      > >excuse this as well as my bad English.
                                      > >
                                      > > You are not talking about taking a flat with the AO7
                                      > >running, are you.
                                      > >And having the AO7 mirror switched off, does it not come into
                                      > >sero position?
                                      > >Or is it just that what you are talking about?
                                      > >
                                      > >Rolf
                                      > >
                                      > >> -----Ursprüngliche Nachricht-----
                                      > >> Von: paulkccd [mailto:pkane2001@...]
                                      > >> Gesendet: Montag, 10. Juni 2002 22:51
                                      > >> An: ccd-newastro@yahoogroups.com
                                      > >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                      > >>
                                      > >>
                                      > >> I guess it all depends on the amount of correction provided
                                      > >by the AO-
                                      > >> 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                      > >> enough. Any errors greater than that and the flat may be offset by a
                                      > >> pixel or more.
                                      > >>
                                      > >> According to SBIG the AO-7 can provide as much as 50 pixels
                                      > >> correction at 2000mm focal length with an ST-7 pixel size. Any flat
                                      > >> frame shifted by this much will be badly offset from where it should
                                      > >> be. Am I missing something?
                                      > >>
                                      > >> -Paul K
                                      > >>
                                      > >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                      > >> > Paul,
                                      > >> >
                                      > >> > The AO7 is still "guide star" dependent..actually more accurate.
                                      > >> > Therefore, I would think that it shouldn't affect flats at all.
                                      > >> > The final results of the "light" image, using an AO7 should be very
                                      > >> > accurate (sub pixel error), so the flat should work just fine.
                                      > >> >
                                      > >> > Randy Nulman
                                      > >> >
                                      > >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                      > >> > > Greg, the problem is possibly caused by the reflections of bright
                                      > >> > > light from your optics. You may want to try to lower the
                                      > >> brightness
                                      > >> > > of the lightbox to get the flat frame to expose for
                                      > >10-20 seconds.
                                      > >> > >
                                      > >> > > :than the actual image depending on
                                      > >> > the
                                      > >> > > mirror position? Seems to me that this would be similar to a
                                      > >> > serious
                                      > >> > > mirror flop in an SCT...
                                      > >> > >
                                      > >> > > -Paul K
                                      > >> > > http://pk.darkhorizons.org
                                    • morrinho@t-online.de
                                      I am with you now Paul and I think you are somehow right. What about creating some kind of Track-List like the ST-6 did in T&A ? There is something else to
                                      Message 18 of 30 , Jun 11, 2002
                                        I am with you now Paul and I think you are somehow right. What about
                                        creating some kind of 'Track-List' like the ST-6 did in T&A ?

                                        There is something else to keep in mind, somebody here on the list told
                                        me some months ago " reduce the reflection% to 20% ", so that the RMS
                                        Wander
                                        is always about <1

                                        Rolf

                                        > I assume that the AO-7 will come to some "home" or zero position when
                                        > not guiding, but that doesn't solve the problem.
                                        >
                                        > Consider what happens when the AO-7 is guiding. Say the tracking
                                        > error in the mount is such that a correction of 10 pixels is
                                        > required. The AO-7 bends the light so as to compensate for the error.
                                        > The result is that now the center of the flat frame has shifted by 10
                                        > pixels from its original location. As AO-7 guides, any correction
                                        > will shift the center of the flat frame by that amount. At the end of
                                        > the exposure, the flat frame will be averaged in to the final image
                                        > at all the shift positions that the AO-7 had to visit while guiding.
                                        >
                                        > As I see it, the way to work around this is to use the
                                        > mount "bumping" for any errors over 1 pixel, while using the AO-7 to
                                        > guide out the errors that are less than 1 pixel in size.
                                        >
                                        > -Paul K
                                        > http://pk.darkhorizons.org
                                        >
                                        >
                                        > --- In ccd-newastro@y..., morrinho@t... wrote:
                                        > > May I ask you something what is perhaps a stupid question so please
                                        > > excuse this as well as my bad English.
                                        > >
                                        > > You are not talking about taking a flat with the AO7 running,
                                        > are you.
                                        > > And having the AO7 mirror switched off, does it not come into sero
                                        > position?
                                        > > Or is it just that what you are talking about?
                                        > >
                                        > > Rolf
                                        > >
                                        > > > -----Ursprüngliche Nachricht-----
                                        > > > Von: paulkccd [mailto:pkane2001@h...]
                                        > > > Gesendet: Montag, 10. Juni 2002 22:51
                                        > > > An: ccd-newastro@y...
                                        > > > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                        > > >
                                        > > >
                                        > > > I guess it all depends on the amount of correction provided by
                                        > the AO-
                                        > > > 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                        > > > enough. Any errors greater than that and the flat may be offset
                                        > by a
                                        > > > pixel or more.
                                        > > >
                                        > > > According to SBIG the AO-7 can provide as much as 50 pixels
                                        > > > correction at 2000mm focal length with an ST-7 pixel size. Any
                                        > flat
                                        > > > frame shifted by this much will be badly offset from where it
                                        > should
                                        > > > be. Am I missing something?
                                        > > >
                                        > > > -Paul K
                                        > > >
                                        > > > --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                        > > > > Paul,
                                        > > > >
                                        > > > > The AO7 is still "guide star" dependent..actually more accurate.
                                        > > > > Therefore, I would think that it shouldn't affect flats at all.
                                        > > > > The final results of the "light" image, using an AO7 should be
                                        > very
                                        > > > > accurate (sub pixel error), so the flat should work just fine.
                                        > > > >
                                        > > > > Randy Nulman
                                        > > > >
                                        > > > > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                        > > > > > Greg, the problem is possibly caused by the reflections of
                                        > bright
                                        > > > > > light from your optics. You may want to try to lower the
                                        > > > brightness
                                        > > > > > of the lightbox to get the flat frame to expose for 10-20
                                        > seconds.
                                        > > > > >
                                        > > > > > Actually, I don't understand how one can take flat-frames
                                        > with an
                                        > > > > AO-
                                        > > > > > 7 in the path. The AO-7 adjusts the image position based on
                                        > > > guiding
                                        > > > > > errors. Wouldn't that mean that the flat-frame can potentially
                                        > > > fall
                                        > > > > > on different pixel coordinates than the actual image
                                        > depending on
                                        > > > > the
                                        > > > > > mirror position? Seems to me that this would be similar to a
                                        > > > > serious
                                        > > > > > mirror flop in an SCT...
                                        > > > > >
                                        > > > > > -Paul K
                                        > > > > > http://pk.darkhorizons.org
                                        > > > > >
                                        > > >
                                        > > >
                                        > > >
                                        > > >
                                        > > > To unsubscribe from this group, send an email to:
                                        > > > ccd-newastro-unsubscribe@e...
                                        > > >
                                        > > >
                                        > > >
                                        > > > Your use of Yahoo! Groups is subject to
                                        > http://docs.yahoo.com/info/terms/
                                        > > >
                                        > > >
                                        >
                                        >
                                        >
                                        > To unsubscribe from this group, send an email to:
                                        > ccd-newastro-unsubscribe@egroups.com
                                        >
                                        >
                                        >
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                                        >
                                        >
                                        >
                                      • Greg Crawford
                                        Rolf, I m not sure. I raised the question on the SBIG users list, where there are many experienced AO-7 users, and no one said that the AO-7, as such, created
                                        Message 19 of 30 , Jun 12, 2002
                                          Rolf,

                                          I'm not sure. I raised the question on the SBIG users list, where there are many
                                          experienced AO-7 users, and no one said that the AO-7, as such, created a
                                          problem for flat fields. In fact, one person said specifically that it does not.

                                          In the meantime, I removed the JMI focuser and the pattern of bad flat changed!
                                          The bar above the circle disappeared and was replaced just by an intense arc on
                                          part of the circle. This is starting to look like an internal reflection problem
                                          and I am wondering whether I need to do some flocking. Any suggestions for
                                          suitable material?

                                          Greg Crawford
                                          Observing from Southern Skies

                                          *

                                          * *
                                          *


                                          *

                                          http://www.nelsonbay.com/~gc/observatory.htm

                                          "Though my soul may set in darkness, it will rise in perfect light,
                                          I have loved the stars too dearly to be fearful of the night."
                                          - from the gravestone of astronomer, John Brashear.




                                          >-----Original Message-----
                                          >From: morrinho@... [mailto:morrinho@...]
                                          >Sent: Wednesday, 12 June 2002 4:32 PM
                                          >To: ccd-newastro@yahoogroups.com
                                          >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                          >
                                          >
                                          >Yes Greg, that is also the software I use and the way I use my AO7 for
                                          >flats. But >with the "AO Enabled" box checked, but not guiding.< the
                                          >AO7 is switched off, isn't it?
                                          >
                                          > I think what I missed up to now is that Paul doubted that the flat
                                          >matches the light which was taken with a "swinging mirror" is
                                          >that correct?
                                          >
                                          >Rolf
                                          >
                                          >> -----Ursprüngliche Nachricht-----
                                          >> Von: Greg Crawford [mailto:gc@...]
                                          >> Gesendet: Dienstag, 11. Juni 2002 17:20
                                          >> An: ccd-newastro@yahoogroups.com
                                          >> Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                          >>
                                          >>
                                          >> Hi Rolf,
                                          >>
                                          >> When you say with the AO-7 running, I am not sure what you mean.
                                          >> I am using
                                          >> CCDSoftV5 AO-7 pre-release. You connect to the camera with the
                                          >> AO-7 physically
                                          >> connected to the camera. Flat-fields are taken, with the "AO
                                          >Enabled" box
                                          >> checked, but not guiding.
                                          >>
                                          >> - Greg
                                          >>
                                          >> >-----Original Message-----
                                          >> >From: morrinho@... [mailto:morrinho@...]
                                          >> >Sent: Wednesday, 12 June 2002 12:45 AM
                                          >> >To: ccd-newastro@yahoogroups.com
                                          >> >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                          >> >
                                          >> >
                                          >> >May I ask you something what is perhaps a stupid question so please
                                          >> >excuse this as well as my bad English.
                                          >> >
                                          >> > You are not talking about taking a flat with the AO7
                                          >> >running, are you.
                                          >> >And having the AO7 mirror switched off, does it not come into
                                          >> >sero position?
                                          >> >Or is it just that what you are talking about?
                                          >> >
                                          >> >Rolf
                                          >> >
                                          >> >> -----Ursprüngliche Nachricht-----
                                          >> >> Von: paulkccd [mailto:pkane2001@...]
                                          >> >> Gesendet: Montag, 10. Juni 2002 22:51
                                          >> >> An: ccd-newastro@yahoogroups.com
                                          >> >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                          >> >>
                                          >> >>
                                          >> >> I guess it all depends on the amount of correction provided
                                          >> >by the AO-
                                          >> >> 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                          >> >> enough. Any errors greater than that and the flat may be
                                          >offset by a
                                          >> >> pixel or more.
                                          >> >>
                                          >> >> According to SBIG the AO-7 can provide as much as 50 pixels
                                          >> >> correction at 2000mm focal length with an ST-7 pixel
                                          >size. Any flat
                                          >> >> frame shifted by this much will be badly offset from
                                          >where it should
                                          >> >> be. Am I missing something?
                                          >> >>
                                          >> >> -Paul K
                                          >> >>
                                          >> >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                          >> >> > Paul,
                                          >> >> >
                                          >> >> > The AO7 is still "guide star" dependent..actually more accurate.
                                          >> >> > Therefore, I would think that it shouldn't affect flats at all.
                                          >> >> > The final results of the "light" image, using an AO7
                                          >should be very
                                          >> >> > accurate (sub pixel error), so the flat should work just fine.
                                          >> >> >
                                          >> >> > Randy Nulman
                                          >> >> >
                                          >> >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                          >> >> > > Greg, the problem is possibly caused by the
                                          >reflections of bright
                                          >> >> > > light from your optics. You may want to try to lower the
                                          >> >> brightness
                                          >> >> > > of the lightbox to get the flat frame to expose for
                                          >> >10-20 seconds.
                                          >> >> > >
                                          >> >> > > :than the actual image depending on
                                          >> >> > the
                                          >> >> > > mirror position? Seems to me that this would be similar to a
                                          >> >> > serious
                                          >> >> > > mirror flop in an SCT...
                                          >> >> > >
                                          >> >> > > -Paul K
                                          >> >> > > http://pk.darkhorizons.org
                                          >
                                          >
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                                        • paulkccd
                                          Yes, the light frame will have uneven illumination shifted from pixel to pixel based on the mirror corrections. A flat frame taken with a static mirror will
                                          Message 20 of 30 , Jun 12, 2002
                                            Yes, the light frame will have uneven illumination shifted from pixel
                                            to pixel based on the mirror corrections. A flat frame taken with a
                                            static mirror will not match all the positions that the uneven
                                            illumination was applied to in the light image.

                                            The track & accummulate list may work, but I think it will be very
                                            difficult to record and replay all the guiding corrections for the
                                            flat frame. The best solution is to limit the mirror to less than 1
                                            pixel movements, and to possibly apply a 1 pixel blur to the flat as
                                            Ron suggested.

                                            -Paul K


                                            --- In ccd-newastro@y..., morrinho@t... wrote:
                                            > Yes Greg, that is also the software I use and the way I use my AO7
                                            for
                                            > flats. But >with the "AO Enabled" box checked, but not guiding.< the
                                            > AO7 is switched off, isn't it?
                                            >
                                            > I think what I missed up to now is that Paul doubted that the flat
                                            > matches the light which was taken with a "swinging mirror" is that
                                            correct?
                                            >
                                            > Rolf
                                          • Ugly Dog
                                            Hi Greg I floced mine with this: http://www.fpi-protostar.com/flocked.htm I like it a lot. And its never had any problem. I think Edmound Scientific might
                                            Message 21 of 30 , Jun 12, 2002
                                              Hi Greg
                                              I floced mine with this:
                                              http://www.fpi-protostar.com/flocked.htm
                                              I like it a lot. And its never had any problem. I think Edmound
                                              Scientific might also have some.
                                              Ugly Dog


                                              --- Greg Crawford <gc@...> wrote:
                                              > Rolf,
                                              >
                                              > I'm not sure. I raised the question on the SBIG users list, where
                                              > there are many
                                              > experienced AO-7 users, and no one said that the AO-7, as such,
                                              > created a
                                              > problem for flat fields. In fact, one person said specifically that
                                              > it does not.
                                              >
                                              > In the meantime, I removed the JMI focuser and the pattern of bad
                                              > flat changed!
                                              > The bar above the circle disappeared and was replaced just by an
                                              > intense arc on
                                              > part of the circle. This is starting to look like an internal
                                              > reflection problem
                                              > and I am wondering whether I need to do some flocking. Any
                                              > suggestions for
                                              > suitable material?
                                              >
                                              > Greg Crawford
                                              > Observing from Southern Skies
                                              >
                                              > *
                                              >
                                              > * *
                                              > *
                                              >
                                              >
                                              > *
                                              >
                                              > http://www.nelsonbay.com/~gc/observatory.htm
                                              >
                                              > "Though my soul may set in darkness, it will rise in perfect light,
                                              > I have loved the stars too dearly to be fearful of the night."
                                              > - from the gravestone of astronomer, John
                                              > Brashear.
                                              >
                                              >
                                              >
                                              >
                                              > >-----Original Message-----
                                              > >From: morrinho@... [mailto:morrinho@...]
                                              > >Sent: Wednesday, 12 June 2002 4:32 PM
                                              > >To: ccd-newastro@yahoogroups.com
                                              > >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                              > >
                                              > >
                                              > >Yes Greg, that is also the software I use and the way I use my AO7
                                              > for
                                              > >flats. But >with the "AO Enabled" box checked, but not guiding.<
                                              > the
                                              > >AO7 is switched off, isn't it?
                                              > >
                                              > > I think what I missed up to now is that Paul doubted that the
                                              > flat
                                              > >matches the light which was taken with a "swinging mirror" is
                                              > >that correct?
                                              > >
                                              > >Rolf
                                              > >
                                              > >> -----Urspr�ngliche Nachricht-----
                                              > >> Von: Greg Crawford [mailto:gc@...]
                                              > >> Gesendet: Dienstag, 11. Juni 2002 17:20
                                              > >> An: ccd-newastro@yahoogroups.com
                                              > >> Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                              > >>
                                              > >>
                                              > >> Hi Rolf,
                                              > >>
                                              > >> When you say with the AO-7 running, I am not sure what you mean.
                                              > >> I am using
                                              > >> CCDSoftV5 AO-7 pre-release. You connect to the camera with the
                                              > >> AO-7 physically
                                              > >> connected to the camera. Flat-fields are taken, with the "AO
                                              > >Enabled" box
                                              > >> checked, but not guiding.
                                              > >>
                                              > >> - Greg
                                              > >>
                                              > >> >-----Original Message-----
                                              > >> >From: morrinho@... [mailto:morrinho@...]
                                              > >> >Sent: Wednesday, 12 June 2002 12:45 AM
                                              > >> >To: ccd-newastro@yahoogroups.com
                                              > >> >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                              > >> >
                                              > >> >
                                              > >> >May I ask you something what is perhaps a stupid question so
                                              > please
                                              > >> >excuse this as well as my bad English.
                                              > >> >
                                              > >> > You are not talking about taking a flat with the AO7
                                              > >> >running, are you.
                                              > >> >And having the AO7 mirror switched off, does it not come into
                                              > >> >sero position?
                                              > >> >Or is it just that what you are talking about?
                                              > >> >
                                              > >> >Rolf
                                              > >> >
                                              > >> >> -----Urspr�ngliche Nachricht-----
                                              > >> >> Von: paulkccd [mailto:pkane2001@...]
                                              > >> >> Gesendet: Montag, 10. Juni 2002 22:51
                                              > >> >> An: ccd-newastro@yahoogroups.com
                                              > >> >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                              > >> >>
                                              > >> >>
                                              > >> >> I guess it all depends on the amount of correction provided
                                              > >> >by the AO-
                                              > >> >> 7. If it's within 1/2 a pixel, the flat is likely to be
                                              > accurate
                                              > >> >> enough. Any errors greater than that and the flat may be
                                              > >offset by a
                                              > >> >> pixel or more.
                                              > >> >>
                                              > >> >> According to SBIG the AO-7 can provide as much as 50 pixels
                                              > >> >> correction at 2000mm focal length with an ST-7 pixel
                                              > >size. Any flat
                                              > >> >> frame shifted by this much will be badly offset from
                                              > >where it should
                                              > >> >> be. Am I missing something?
                                              > >> >>
                                              > >> >> -Paul K
                                              > >> >>
                                              > >> >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...>
                                              > wrote:
                                              > >> >> > Paul,
                                              > >> >> >
                                              > >> >> > The AO7 is still "guide star" dependent..actually more
                                              > accurate.
                                              > >> >> > Therefore, I would think that it shouldn't affect flats at
                                              > all.
                                              > >> >> > The final results of the "light" image, using an AO7
                                              > >should be very
                                              > >> >> > accurate (sub pixel error), so the flat should work just
                                              > fine.
                                              > >> >> >
                                              > >> >> > Randy Nulman
                                              > >> >> >
                                              > >> >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...>
                                              > wrote:
                                              > >> >> > > Greg, the problem is possibly caused by the
                                              > >reflections of bright
                                              > >> >> > > light from your optics. You may want to try to lower the
                                              > >> >> brightness
                                              > >> >> > > of the lightbox to get the flat frame to expose for
                                              > >> >10-20 seconds.
                                              > >> >> > >
                                              > >> >> > > :than the actual image depending on
                                              > >> >> > the
                                              > >> >> > > mirror position? Seems to me that this would be similar
                                              > to a
                                              > >> >> > serious
                                              > >> >> > > mirror flop in an SCT...
                                              > >> >> > >
                                              > >> >> > > -Paul K
                                              > >> >> > > http://pk.darkhorizons.org
                                              > >
                                              > >
                                              > >------------------------ Yahoo! Groups Sponsor
                                              > >---------------------~-->
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                                              > >Will You Meet the One?
                                              > >Free Love Reading by phone!
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                                              > >
                                              > >
                                              > >
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                                              Ugly Dog
                                              http://www.bewellweb.com/g42016k/astro.htm

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                                            • Matt Russell
                                              Greg, I had the same issue with a JMI NGFs focuser. There were light reflections within the mechanism and once I flocked the entire inner barrel, the problem
                                              Message 22 of 30 , Jun 12, 2002
                                                Greg,

                                                I had the same issue with a JMI NGFs focuser. There were light reflections
                                                within the mechanism and once I flocked the entire inner barrel, the problem
                                                was gone. Actually, I flocked anything on that focuser that could
                                                potentially cause light to bounce around.

                                                They were made aware of this issue and now supply the JMI with a sleeve that
                                                supposedly takes care of the problem.

                                                Matt Russell
                                                http://www.telescopes.cc
                                              • randy_nulman
                                                FWIW, I got mine from Edmund Scientific (self adhesive version) and it s worked great! No peeling, even thru various temp. extremes, and no flaking noticed
                                                Message 23 of 30 , Jun 12, 2002
                                                  FWIW, I got mine from Edmund Scientific (self adhesive version) and
                                                  it's worked great! No peeling, even thru various temp. extremes, and
                                                  no flaking noticed after a _long_ period of time.

                                                  Randy

                                                  --- In ccd-newastro@y..., Ugly Dog <shenzistiber@y...> wrote:
                                                  > Hi Greg
                                                  > I floced mine with this:
                                                  > http://www.fpi-protostar.com/flocked.htm
                                                  > I like it a lot. And its never had any problem. I think Edmound
                                                  > Scientific might also have some.
                                                  > Ugly Dog
                                                  >
                                                  >
                                                  > --- Greg Crawford <gc@n...> wrote:
                                                  > > Rolf,
                                                  > >
                                                  > > I'm not sure. I raised the question on the SBIG users list, where
                                                  > > there are many
                                                  > > experienced AO-7 users, and no one said that the AO-7, as such,
                                                  > > created a
                                                  > > problem for flat fields. In fact, one person said specifically
                                                  that
                                                  > > it does not.
                                                  > >
                                                  > > In the meantime, I removed the JMI focuser and the pattern of bad
                                                  > > flat changed!
                                                  > > The bar above the circle disappeared and was replaced just by an
                                                  > > intense arc on
                                                  > > part of the circle. This is starting to look like an internal
                                                  > > reflection problem
                                                  > > and I am wondering whether I need to do some flocking. Any
                                                  > > suggestions for
                                                  > > suitable material?
                                                  > >
                                                  > > Greg Crawford
                                                  > > Observing from Southern Skies
                                                  > >
                                                  > > *
                                                  > >
                                                  > > * *
                                                  > > *
                                                  > >
                                                  > >
                                                  > > *
                                                  > >
                                                  > > http://www.nelsonbay.com/~gc/observatory.htm
                                                  > >
                                                  > > "Though my soul may set in darkness, it will rise in perfect
                                                  light,
                                                  > > I have loved the stars too dearly to be fearful of the night."
                                                  > > - from the gravestone of astronomer, John
                                                  > > Brashear.
                                                  > >
                                                  > >
                                                  > >
                                                  > >
                                                  > > >-----Original Message-----
                                                  > > >From: morrinho@t... [mailto:morrinho@t...]
                                                  > > >Sent: Wednesday, 12 June 2002 4:32 PM
                                                  > > >To: ccd-newastro@y...
                                                  > > >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                  > > >
                                                  > > >
                                                  > > >Yes Greg, that is also the software I use and the way I use my
                                                  AO7
                                                  > > for
                                                  > > >flats. But >with the "AO Enabled" box checked, but not guiding.<
                                                  > > the
                                                  > > >AO7 is switched off, isn't it?
                                                  > > >
                                                  > > > I think what I missed up to now is that Paul doubted that the
                                                  > > flat
                                                  > > >matches the light which was taken with a "swinging mirror" is
                                                  > > >that correct?
                                                  > > >
                                                  > > >Rolf
                                                  > > >
                                                  > > >> -----Ursprüngliche Nachricht-----
                                                  > > >> Von: Greg Crawford [mailto:gc@n...]
                                                  > > >> Gesendet: Dienstag, 11. Juni 2002 17:20
                                                  > > >> An: ccd-newastro@y...
                                                  > > >> Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                  > > >>
                                                  > > >>
                                                  > > >> Hi Rolf,
                                                  > > >>
                                                  > > >> When you say with the AO-7 running, I am not sure what you
                                                  mean.
                                                  > > >> I am using
                                                  > > >> CCDSoftV5 AO-7 pre-release. You connect to the camera with the
                                                  > > >> AO-7 physically
                                                  > > >> connected to the camera. Flat-fields are taken, with the "AO
                                                  > > >Enabled" box
                                                  > > >> checked, but not guiding.
                                                  > > >>
                                                  > > >> - Greg
                                                  > > >>
                                                  > > >> >-----Original Message-----
                                                  > > >> >From: morrinho@t... [mailto:morrinho@t...]
                                                  > > >> >Sent: Wednesday, 12 June 2002 12:45 AM
                                                  > > >> >To: ccd-newastro@y...
                                                  > > >> >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                  > > >> >
                                                  > > >> >
                                                  > > >> >May I ask you something what is perhaps a stupid question so
                                                  > > please
                                                  > > >> >excuse this as well as my bad English.
                                                  > > >> >
                                                  > > >> > You are not talking about taking a flat with the AO7
                                                  > > >> >running, are you.
                                                  > > >> >And having the AO7 mirror switched off, does it not come into
                                                  > > >> >sero position?
                                                  > > >> >Or is it just that what you are talking about?
                                                  > > >> >
                                                  > > >> >Rolf
                                                  > > >> >
                                                  > > >> >> -----Ursprüngliche Nachricht-----
                                                  > > >> >> Von: paulkccd [mailto:pkane2001@h...]
                                                  > > >> >> Gesendet: Montag, 10. Juni 2002 22:51
                                                  > > >> >> An: ccd-newastro@y...
                                                  > > >> >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                  > > >> >>
                                                  > > >> >>
                                                  > > >> >> I guess it all depends on the amount of correction provided
                                                  > > >> >by the AO-
                                                  > > >> >> 7. If it's within 1/2 a pixel, the flat is likely to be
                                                  > > accurate
                                                  > > >> >> enough. Any errors greater than that and the flat may be
                                                  > > >offset by a
                                                  > > >> >> pixel or more.
                                                  > > >> >>
                                                  > > >> >> According to SBIG the AO-7 can provide as much as 50 pixels
                                                  > > >> >> correction at 2000mm focal length with an ST-7 pixel
                                                  > > >size. Any flat
                                                  > > >> >> frame shifted by this much will be badly offset from
                                                  > > >where it should
                                                  > > >> >> be. Am I missing something?
                                                  > > >> >>
                                                  > > >> >> -Paul K
                                                  > > >> >>
                                                  > > >> >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...>
                                                  > > wrote:
                                                  > > >> >> > Paul,
                                                  > > >> >> >
                                                  > > >> >> > The AO7 is still "guide star" dependent..actually more
                                                  > > accurate.
                                                  > > >> >> > Therefore, I would think that it shouldn't affect flats at
                                                  > > all.
                                                  > > >> >> > The final results of the "light" image, using an AO7
                                                  > > >should be very
                                                  > > >> >> > accurate (sub pixel error), so the flat should work just
                                                  > > fine.
                                                  > > >> >> >
                                                  > > >> >> > Randy Nulman
                                                  > > >> >> >
                                                  > > >> >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...>
                                                  > > wrote:
                                                  > > >> >> > > Greg, the problem is possibly caused by the
                                                  > > >reflections of bright
                                                  > > >> >> > > light from your optics. You may want to try to lower the
                                                  > > >> >> brightness
                                                  > > >> >> > > of the lightbox to get the flat frame to expose for
                                                  > > >> >10-20 seconds.
                                                  > > >> >> > >
                                                  > > >> >> > > :than the actual image depending on
                                                  > > >> >> > the
                                                  > > >> >> > > mirror position? Seems to me that this would be similar
                                                  > > to a
                                                  > > >> >> > serious
                                                  > > >> >> > > mirror flop in an SCT...
                                                  > > >> >> > >
                                                  > > >> >> > > -Paul K
                                                  > > >> >> > > http://pk.darkhorizons.org
                                                  > > >
                                                  > > >
                                                  > > >------------------------ Yahoo! Groups Sponsor
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                                                  > > >------~->
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                                                  > > >To unsubscribe from this group, send an email to:
                                                  > > >ccd-newastro-unsubscribe@e...
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                                                  > > >
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                                                  > >
                                                  > >
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                                                  > =====
                                                  > Ugly Dog
                                                  > http://www.bewellweb.com/g42016k/astro.htm
                                                  >
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                                                • morrinho@t-online.de
                                                  Hi Paul, did you actually see some problems in the flat of the AO7 ? And do you have an idea which program might be able to do a 1 pixel blur? Rolf
                                                  Message 24 of 30 , Jun 13, 2002
                                                    Hi Paul,

                                                    did you actually see some problems in the flat of the AO7 ?

                                                    And do you have an idea which program might be able to do a 1 pixel blur?

                                                    Rolf

                                                    >
                                                    > Yes, the light frame will have uneven illumination shifted from pixel
                                                    > to pixel based on the mirror corrections. A flat frame taken with a
                                                    > static mirror will not match all the positions that the uneven
                                                    > illumination was applied to in the light image.
                                                    >
                                                    > The track & accummulate list may work, but I think it will be very
                                                    > difficult to record and replay all the guiding corrections for the
                                                    > flat frame. The best solution is to limit the mirror to less than 1
                                                    > pixel movements, and to possibly apply a 1 pixel blur to the flat as
                                                    > Ron suggested.
                                                    >
                                                    > -Paul K
                                                    >
                                                    >
                                                    > --- In ccd-newastro@y..., morrinho@t... wrote:
                                                    > > Yes Greg, that is also the software I use and the way I use my AO7
                                                    > for
                                                    > > flats. But >with the "AO Enabled" box checked, but not guiding.< the
                                                    > > AO7 is switched off, isn't it?
                                                    > >
                                                    > > I think what I missed up to now is that Paul doubted that the flat
                                                    > > matches the light which was taken with a "swinging mirror" is that
                                                    > correct?
                                                    > >
                                                    > > Rolf
                                                  • morrinho@t-online.de
                                                    Hi Greg, I had the same problems with me focuser. Could not get proper flocking stuff here in Germany, so I painted it with school-blackboard-paint, worked
                                                    Message 25 of 30 , Jun 13, 2002
                                                      Hi Greg,

                                                      I had the same problems with me focuser. Could not get proper flocking stuff
                                                      here in Germany, so I painted it with school-blackboard-paint, worked well.

                                                      But let me tell you something else, my Meade 6.3 reducer caused also
                                                      reflections
                                                      near bright objects/stars. A friend gave me his Celestron reducer and the
                                                      reflections
                                                      are more or less gone -only stars like Vega show a very dim circle. Do you
                                                      have a Meade 6.3
                                                      in your train?

                                                      Rolf

                                                      >
                                                      > Rolf,
                                                      >
                                                      > I'm not sure. I raised the question on the SBIG users list, where
                                                      > there are many
                                                      > experienced AO-7 users, and no one said that the AO-7, as such, created a
                                                      > problem for flat fields. In fact, one person said specifically
                                                      > that it does not.
                                                      >
                                                      > In the meantime, I removed the JMI focuser and the pattern of bad
                                                      > flat changed!
                                                      > The bar above the circle disappeared and was replaced just by an
                                                      > intense arc on
                                                      > part of the circle. This is starting to look like an internal
                                                      > reflection problem
                                                      > and I am wondering whether I need to do some flocking. Any suggestions for
                                                      > suitable material?
                                                      >
                                                      > Greg Crawford
                                                      > Observing from Southern Skies
                                                      >
                                                      > *
                                                      >
                                                      > * *
                                                      > *
                                                      >
                                                      >
                                                      > *
                                                      >
                                                      > http://www.nelsonbay.com/~gc/observatory.htm
                                                      >
                                                      > "Though my soul may set in darkness, it will rise in perfect light,
                                                      > I have loved the stars too dearly to be fearful of the night."
                                                      > - from the gravestone of astronomer, John Brashear.
                                                      >
                                                      >
                                                      >
                                                      >
                                                      > >-----Original Message-----
                                                      > >From: morrinho@... [mailto:morrinho@...]
                                                      > >Sent: Wednesday, 12 June 2002 4:32 PM
                                                      > >To: ccd-newastro@yahoogroups.com
                                                      > >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                      > >
                                                      > >
                                                      > >Yes Greg, that is also the software I use and the way I use my AO7 for
                                                      > >flats. But >with the "AO Enabled" box checked, but not guiding.< the
                                                      > >AO7 is switched off, isn't it?
                                                      > >
                                                      > > I think what I missed up to now is that Paul doubted that the flat
                                                      > >matches the light which was taken with a "swinging mirror" is
                                                      > >that correct?
                                                      > >
                                                      > >Rolf
                                                      > >
                                                      > >> -----Ursprüngliche Nachricht-----
                                                      > >> Von: Greg Crawford [mailto:gc@...]
                                                      > >> Gesendet: Dienstag, 11. Juni 2002 17:20
                                                      > >> An: ccd-newastro@yahoogroups.com
                                                      > >> Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                      > >>
                                                      > >>
                                                      > >> Hi Rolf,
                                                      > >>
                                                      > >> When you say with the AO-7 running, I am not sure what you mean.
                                                      > >> I am using
                                                      > >> CCDSoftV5 AO-7 pre-release. You connect to the camera with the
                                                      > >> AO-7 physically
                                                      > >> connected to the camera. Flat-fields are taken, with the "AO
                                                      > >Enabled" box
                                                      > >> checked, but not guiding.
                                                      > >>
                                                      > >> - Greg
                                                      > >>
                                                      > >> >-----Original Message-----
                                                      > >> >From: morrinho@... [mailto:morrinho@...]
                                                      > >> >Sent: Wednesday, 12 June 2002 12:45 AM
                                                      > >> >To: ccd-newastro@yahoogroups.com
                                                      > >> >Subject: AW: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                      > >> >
                                                      > >> >
                                                      > >> >May I ask you something what is perhaps a stupid question so please
                                                      > >> >excuse this as well as my bad English.
                                                      > >> >
                                                      > >> > You are not talking about taking a flat with the AO7
                                                      > >> >running, are you.
                                                      > >> >And having the AO7 mirror switched off, does it not come into
                                                      > >> >sero position?
                                                      > >> >Or is it just that what you are talking about?
                                                      > >> >
                                                      > >> >Rolf
                                                      > >> >
                                                      > >> >> -----Ursprüngliche Nachricht-----
                                                      > >> >> Von: paulkccd [mailto:pkane2001@...]
                                                      > >> >> Gesendet: Montag, 10. Juni 2002 22:51
                                                      > >> >> An: ccd-newastro@yahoogroups.com
                                                      > >> >> Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                      > >> >>
                                                      > >> >>
                                                      > >> >> I guess it all depends on the amount of correction provided
                                                      > >> >by the AO-
                                                      > >> >> 7. If it's within 1/2 a pixel, the flat is likely to be accurate
                                                      > >> >> enough. Any errors greater than that and the flat may be
                                                      > >offset by a
                                                      > >> >> pixel or more.
                                                      > >> >>
                                                      > >> >> According to SBIG the AO-7 can provide as much as 50 pixels
                                                      > >> >> correction at 2000mm focal length with an ST-7 pixel
                                                      > >size. Any flat
                                                      > >> >> frame shifted by this much will be badly offset from
                                                      > >where it should
                                                      > >> >> be. Am I missing something?
                                                      > >> >>
                                                      > >> >> -Paul K
                                                      > >> >>
                                                      > >> >> --- In ccd-newastro@y..., "randy_nulman" <rjnulman@w...> wrote:
                                                      > >> >> > Paul,
                                                      > >> >> >
                                                      > >> >> > The AO7 is still "guide star" dependent..actually more accurate.
                                                      > >> >> > Therefore, I would think that it shouldn't affect flats at all.
                                                      > >> >> > The final results of the "light" image, using an AO7
                                                      > >should be very
                                                      > >> >> > accurate (sub pixel error), so the flat should work just fine.
                                                      > >> >> >
                                                      > >> >> > Randy Nulman
                                                      > >> >> >
                                                      > >> >> > --- In ccd-newastro@y..., "paulkccd" <pkane2001@h...> wrote:
                                                      > >> >> > > Greg, the problem is possibly caused by the
                                                      > >reflections of bright
                                                      > >> >> > > light from your optics. You may want to try to lower the
                                                      > >> >> brightness
                                                      > >> >> > > of the lightbox to get the flat frame to expose for
                                                      > >> >10-20 seconds.
                                                      > >> >> > >
                                                      > >> >> > > :than the actual image depending on
                                                      > >> >> > the
                                                      > >> >> > > mirror position? Seems to me that this would be similar to a
                                                      > >> >> > serious
                                                      > >> >> > > mirror flop in an SCT...
                                                      > >> >> > >
                                                      > >> >> > > -Paul K
                                                      > >> >> > > http://pk.darkhorizons.org
                                                      > >
                                                      > >
                                                      > >------------------------ Yahoo! Groups Sponsor
                                                      > >---------------------~-->
                                                      > >Will You Find True Love?
                                                      > >Will You Meet the One?
                                                      > >Free Love Reading by phone!
                                                      > >http://us.click.yahoo.com/Deo18C/zDLEAA/Ey.GAA/N_XolB/TM
                                                      > >---------------------------------------------------------------
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                                                      > >
                                                      > >To unsubscribe from this group, send an email to:
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                                                      > >
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                                                      > http://docs.yahoo.com/info/terms/
                                                      >
                                                      >
                                                      >
                                                      >
                                                      >
                                                      >
                                                      > To unsubscribe from this group, send an email to:
                                                      > ccd-newastro-unsubscribe@egroups.com
                                                      >
                                                      >
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                                                      >
                                                      >
                                                      >
                                                    • paulkccd
                                                      Rolf, the discussion was purely theoretical from my side . I have not seen or even heard of problems caused by an AO-7 in the flats. I can be totally wrong
                                                      Message 26 of 30 , Jun 13, 2002
                                                        Rolf, the discussion was purely theoretical from my side <g>. I have
                                                        not seen or even heard of problems caused by an AO-7 in the flats. I
                                                        can be totally wrong about this, but I don't see how it can work any
                                                        other way.

                                                        Photoshop and Maxim, among others can do a 1 pixel blur.

                                                        -Paul K

                                                        --- In ccd-newastro@y..., morrinho@t... wrote:
                                                        > Hi Paul,
                                                        >
                                                        > did you actually see some problems in the flat of the AO7 ?
                                                        >
                                                        > And do you have an idea which program might be able to do a 1 pixel
                                                        blur?
                                                        >
                                                        > Rolf
                                                        >
                                                        > >
                                                        > > Yes, the light frame will have uneven illumination shifted from
                                                        pixel
                                                        > > to pixel based on the mirror corrections. A flat frame taken with
                                                        a
                                                        > > static mirror will not match all the positions that the uneven
                                                        > > illumination was applied to in the light image.
                                                        > >
                                                        > > The track & accummulate list may work, but I think it will be
                                                        very
                                                        > > difficult to record and replay all the guiding corrections for
                                                        the
                                                        > > flat frame. The best solution is to limit the mirror to less than
                                                        1
                                                        > > pixel movements, and to possibly apply a 1 pixel blur to the flat
                                                        as
                                                        > > Ron suggested.
                                                        > >
                                                        > > -Paul K
                                                      • Greg Crawford
                                                        ... Hi Rolf, No, I own a Celestron reducer, but do not use it because it created strange reflections on the image. My main goals are hunting asteroids and
                                                        Message 27 of 30 , Jun 13, 2002
                                                          >Do you have a Meade 6.3in your train?
                                                          >
                                                          >Rolf

                                                          Hi Rolf,

                                                          No, I own a Celestron reducer, but do not use it because it created strange
                                                          reflections on the image. My main goals are hunting asteroids and photometry,
                                                          and as I believe the best optical results, (including signal-to-noise), are
                                                          obtained using any scope at its intended focal ratio, I only use the focal
                                                          reducer as a screw-on dust cap when my camera has been removed. :-)

                                                          I am hunting down sources of flocking paper in order to experiment with it, at
                                                          the moment. Thanks for your suggestions to-date.

                                                          - Greg
                                                        • morrinho@t-online.de
                                                          Hello Greg, may be this mail Neil Martin -how are you doing Neil- once wrote me will ... flocking is a two part application. You paint an adhesive first, then
                                                          Message 28 of 30 , Jun 13, 2002
                                                            Hello Greg,

                                                            may be this mail Neil Martin -how are you doing Neil- once wrote me will
                                                            help you:

                                                            >>Hello Rolf, I am sorry for the delay; I have been away on holiday. The
                                                            flocking is a two part application. You paint an adhesive first, then you
                                                            apply some very small fibers to it. This works very good and is the best way
                                                            that I have seen. The flocking kit is made by Plaid Enterprises, Inc.
                                                            Norcross, GA USA 30091-7600. Their web site is www.plaidonline.com. I
                                                            purchased it at a craft store in Colorado, which is close to New Mexico, so
                                                            it should be available to your friend.
                                                            I just made up a f3.3 focal reducer tonight and am anxious for some clear
                                                            skies to try it out. Good luck Rolf and happy holidays. Neil Martin <<

                                                            Rolf


                                                            > -----Ursprüngliche Nachricht-----
                                                            > Von: Greg Crawford [mailto:gc@...]
                                                            > Gesendet: Freitag, 14. Juni 2002 01:36
                                                            > An: ccd-newastro@yahoogroups.com
                                                            > Betreff: RE: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                            >
                                                            >
                                                            > >Do you have a Meade 6.3in your train?
                                                            > >
                                                            > >Rolf
                                                            >
                                                            > Hi Rolf,
                                                            >
                                                            > No, I own a Celestron reducer, but do not use it because it
                                                            > created strange
                                                            > reflections on the image. My main goals are hunting asteroids and
                                                            > photometry,
                                                            > and as I believe the best optical results, (including
                                                            > signal-to-noise), are
                                                            > obtained using any scope at its intended focal ratio, I only use the focal
                                                            > reducer as a screw-on dust cap when my camera has been removed. :-)
                                                            >
                                                            > I am hunting down sources of flocking paper in order to
                                                            > experiment with it, at
                                                            > the moment. Thanks for your suggestions to-date.
                                                            >
                                                            > - Greg
                                                            >
                                                            >
                                                            >
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                                                          • morrinho@t-online.de
                                                            Thank you Paul for the advice, I ll try it and will have a look if it comes out any better. Rolf
                                                            Message 29 of 30 , Jun 13, 2002
                                                              Thank you Paul for the advice, I'll try it and will have
                                                              a look if it comes out any better.

                                                              Rolf

                                                              > -----Ursprüngliche Nachricht-----
                                                              > Von: paulkccd [mailto:pkane2001@...]
                                                              > Gesendet: Donnerstag, 13. Juni 2002 20:47
                                                              > An: ccd-newastro@yahoogroups.com
                                                              > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                              >
                                                              >
                                                              > Rolf, the discussion was purely theoretical from my side <g>. I have
                                                              > not seen or even heard of problems caused by an AO-7 in the flats. I
                                                              > can be totally wrong about this, but I don't see how it can work any
                                                              > other way.
                                                              >
                                                              > Photoshop and Maxim, among others can do a 1 pixel blur.
                                                              >
                                                              > -Paul K
                                                              >
                                                              > --- In ccd-newastro@y..., morrinho@t... wrote:
                                                              > > Hi Paul,
                                                              > >
                                                              > > did you actually see some problems in the flat of the AO7 ?
                                                              > >
                                                              > > And do you have an idea which program might be able to do a 1 pixel
                                                              > blur?
                                                              > >
                                                              > > Rolf
                                                              > >
                                                              > > >
                                                              > > > Yes, the light frame will have uneven illumination shifted from
                                                              > pixel
                                                              > > > to pixel based on the mirror corrections. A flat frame taken with
                                                              > a
                                                              > > > static mirror will not match all the positions that the uneven
                                                              > > > illumination was applied to in the light image.
                                                              > > >
                                                              > > > The track & accummulate list may work, but I think it will be
                                                              > very
                                                              > > > difficult to record and replay all the guiding corrections for
                                                              > the
                                                              > > > flat frame. The best solution is to limit the mirror to less than
                                                              > 1
                                                              > > > pixel movements, and to possibly apply a 1 pixel blur to the flat
                                                              > as
                                                              > > > Ron suggested.
                                                              > > >
                                                              > > > -Paul K
                                                              >
                                                              >
                                                              >
                                                              >
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                                                              > ccd-newastro-unsubscribe@egroups.com
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                                                            • fussylizard
                                                              I regularly image with an AO-7, and I have not had any problems with flats- they work fine. Based on how the system works, I agree there is a potential for
                                                              Message 30 of 30 , Jun 14, 2002
                                                                I regularly image with an AO-7, and I have not had any problems with
                                                                flats- they work fine. Based on how the system works, I agree there
                                                                is a potential for "suboptimal" flats given the moving mirror. I've
                                                                not done a detailed comparison of images with and without the AO-7 to
                                                                determine the actual differences, but it looks good to me, at least
                                                                for "pretty pictures". Besides, I'd think the better tracking to be
                                                                had with an AO-7 would likely offset any small defects in the flats.

                                                                Regards,
                                                                Chris Durand

                                                                --- In ccd-newastro@y..., morrinho@t... wrote:
                                                                > Thank you Paul for the advice, I'll try it and will have
                                                                > a look if it comes out any better.
                                                                >
                                                                > Rolf
                                                                >
                                                                > > -----Ursprüngliche Nachricht-----
                                                                > > Von: paulkccd [mailto:pkane2001@h...]
                                                                > > Gesendet: Donnerstag, 13. Juni 2002 20:47
                                                                > > An: ccd-newastro@y...
                                                                > > Betreff: [ccd-newastro] Re: Hi and Flat-Field Problem
                                                                > >
                                                                > >
                                                                > > Rolf, the discussion was purely theoretical from my side <g>. I
                                                                have
                                                                > > not seen or even heard of problems caused by an AO-7 in the
                                                                flats. I
                                                                > > can be totally wrong about this, but I don't see how it can work
                                                                any
                                                                > > other way.
                                                                > >
                                                                > > Photoshop and Maxim, among others can do a 1 pixel blur.
                                                                > >
                                                                > > -Paul K
                                                                > >
                                                                > > --- In ccd-newastro@y..., morrinho@t... wrote:
                                                                > > > Hi Paul,
                                                                > > >
                                                                > > > did you actually see some problems in the flat of the AO7 ?
                                                                > > >
                                                                > > > And do you have an idea which program might be able to do a 1
                                                                pixel
                                                                > > blur?
                                                                > > >
                                                                > > > Rolf
                                                                > > >
                                                                > > > >
                                                                > > > > Yes, the light frame will have uneven illumination shifted
                                                                from
                                                                > > pixel
                                                                > > > > to pixel based on the mirror corrections. A flat frame taken
                                                                with
                                                                > > a
                                                                > > > > static mirror will not match all the positions that the uneven
                                                                > > > > illumination was applied to in the light image.
                                                                > > > >
                                                                > > > > The track & accummulate list may work, but I think it will be
                                                                > > very
                                                                > > > > difficult to record and replay all the guiding corrections for
                                                                > > the
                                                                > > > > flat frame. The best solution is to limit the mirror to less
                                                                than
                                                                > > 1
                                                                > > > > pixel movements, and to possibly apply a 1 pixel blur to the
                                                                flat
                                                                > > as
                                                                > > > > Ron suggested.
                                                                > > > >
                                                                > > > > -Paul K
                                                                > >
                                                                > >
                                                                > >
                                                                > >
                                                                > > To unsubscribe from this group, send an email to:
                                                                > > ccd-newastro-unsubscribe@e...
                                                                > >
                                                                > >
                                                                > >
                                                                > > Your use of Yahoo! Groups is subject to
                                                                http://docs.yahoo.com/info/terms/
                                                                > >
                                                                > >
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