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What the heck....a donut near M81?

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  • mike_from_tn@yahoo.com
    Would greatly appreciate any insight regarding this gremlin in my image. http://personalpages.tds.net/~mfleenor/st10/m81_150min-Irblock.jpg This is 15 x 600sec
    Message 1 of 10 , Feb 1, 2004
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      Would greatly appreciate any insight regarding this gremlin in my
      image.


      http://personalpages.tds.net/~mfleenor/st10/m81_150min-Irblock.jpg

      This is 15 x 600sec with a Schuler Ir block.
      ST10 XME/ Intes MK69

      I took a good set of flat frames and checking the individual flats
      against the master doesn't reveal anything however after calibrating
      the individual image frames I get the donut pattern. Anybody seen
      this before?

      Thanks,

      Mike
    • aajohnah
      Not an expert here but looks like it came from the flats, where they either added, it or did not subtract it from the original image Mark ... From:
      Message 2 of 10 , Feb 1, 2004
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        Not an expert here but looks like it came from the flats, where they either
        added, it or did not subtract it from the original image

        Mark
        ----- Original Message -----
        From: <mike_from_tn@...>
        To: <ccd-newastro@yahoogroups.com>
        Sent: Sunday, February 01, 2004 9:55 AM
        Subject: [ccd-newastro] What the heck....a donut near M81?


        > Would greatly appreciate any insight regarding this gremlin in my
        > image.
        >
        >
        > http://personalpages.tds.net/~mfleenor/st10/m81_150min-Irblock.jpg
        >
        > This is 15 x 600sec with a Schuler Ir block.
        > ST10 XME/ Intes MK69
        >
        > I took a good set of flat frames and checking the individual flats
        > against the master doesn't reveal anything however after calibrating
        > the individual image frames I get the donut pattern. Anybody seen
        > this before?
        >
        > Thanks,
        >
        > Mike
        >
        >
        >
        >
        >
        > Yahoo! Groups Links
        >
        > To visit your group on the web, go to:
        > http://groups.yahoo.com/group/ccd-newastro/
        >
        > To unsubscribe from this group, send an email to:
        > ccd-newastro-unsubscribe@yahoogroups.com
        >
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        > http://docs.yahoo.com/info/terms/
        >
        >
        >
      • Wodaski - Yahoo
        A bright, offset circle like that usually indicates that, at the time the flats were taken, there was some back illumination from the focuser/camera end of
        Message 3 of 10 , Feb 1, 2004
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          A bright, offset circle like that usually indicates that, at the time the
          flats were taken, there was some back illumination from the focuser/camera
          end of things. This causes a reflection off of some dust (fairly far from
          the camera in this case because it is so large), leaving a bright spot when
          the flat is applied.

          This typically occurs either when flats are taken in daylight or dusk
          conditions, or any time the light source can enter the back end of the
          scope.


          Ron Wodaski
          The New CCD Astronomy Book
          web site: http://www.newastro.com


          -----Original Message-----
          From: mike_from_tn@... [mailto:mike_from_tn@...]
          Sent: Sunday, February 01, 2004 7:55 AM
          To: ccd-newastro@yahoogroups.com
          Subject: [ccd-newastro] What the heck....a donut near M81?

          Would greatly appreciate any insight regarding this gremlin in my
          image.


          http://personalpages.tds.net/~mfleenor/st10/m81_150min-Irblock.jpg

          This is 15 x 600sec with a Schuler Ir block.
          ST10 XME/ Intes MK69

          I took a good set of flat frames and checking the individual flats
          against the master doesn't reveal anything however after calibrating
          the individual image frames I get the donut pattern. Anybody seen
          this before?

          Thanks,

          Mike





          Yahoo! Groups Links

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        • Mark de Regt
          To add to Ron s information, I always take dawn flats, and I do my best to wrap dark, thick cloth (black corduroy from a cloth store is cheap and effective)
          Message 4 of 10 , Feb 1, 2004
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            To add to Ron's information, I always take dawn flats, and I do my best to
            wrap dark, thick cloth (black corduroy from a cloth store is cheap and
            effective) around all places where light could enter the system (other than
            the front of the scope, of course). I actually keep it wrapped all night,
            too, since there are too many places in my system where stray light enters
            when given the opportunity.

            Mark de Regt
            Redmond, Washington, USA
            47.7 N. Latitude; 122 West Longitude
            Astro Images: http://home.earthlink.net/~akilla/MAD


            > -----Original Message-----
            > From: Wodaski - Yahoo [mailto:yahoo@...]
            > Sent: Sunday, February 01, 2004 7:27 AM
            > To: ccd-newastro@yahoogroups.com
            > Subject: RE: [ccd-newastro] What the heck....a donut near M81?
            >
            >
            > A bright, offset circle like that usually indicates that, at the time the
            > flats were taken, there was some back illumination from the focuser/camera
            > end of things. This causes a reflection off of some dust (fairly far from
            > the camera in this case because it is so large), leaving a bright
            > spot when
            > the flat is applied.
            >
            > This typically occurs either when flats are taken in daylight or dusk
            > conditions, or any time the light source can enter the back end of the
            > scope.
            >
            >
            > Ron Wodaski
            > The New CCD Astronomy Book
            > web site: http://www.newastro.com
            >
            >
            > -----Original Message-----
            > From: mike_from_tn@... [mailto:mike_from_tn@...]
            > Sent: Sunday, February 01, 2004 7:55 AM
            > To: ccd-newastro@yahoogroups.com
            > Subject: [ccd-newastro] What the heck....a donut near M81?
            >
            > Would greatly appreciate any insight regarding this gremlin in my
            > image.
            >
            >
            > http://personalpages.tds.net/~mfleenor/st10/m81_150min-Irblock.jpg
            >
            > This is 15 x 600sec with a Schuler Ir block.
            > ST10 XME/ Intes MK69
            >
            > I took a good set of flat frames and checking the individual flats
            > against the master doesn't reveal anything however after calibrating
            > the individual image frames I get the donut pattern. Anybody seen
            > this before?
            >
            > Thanks,
            >
            > Mike
            >
            >
            >
            >
            >
            > Yahoo! Groups Links
            >
            > To visit your group on the web, go to:
            > http://groups.yahoo.com/group/ccd-newastro/
            >
            > To unsubscribe from this group, send an email to:
            > ccd-newastro-unsubscribe@yahoogroups.com
            >
            > Your use of Yahoo! Groups is subject to:
            > http://docs.yahoo.com/info/terms/
            >
            >
            >
            >
            >
            >
            >
            > Yahoo! Groups Links
            >
            > To visit your group on the web, go to:
            > http://groups.yahoo.com/group/ccd-newastro/
            >
            > To unsubscribe from this group, send an email to:
            > ccd-newastro-unsubscribe@yahoogroups.com
            >
            > Your use of Yahoo! Groups is subject to:
            > http://docs.yahoo.com/info/terms/
            >
            >
          • rdcrisp
            ... time the ... focuser/camera ... far from ... spot when ... dusk ... the ... I ve had the same problem as Ron described. I cured it by wrapping things with
            Message 5 of 10 , Feb 1, 2004
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              --- In ccd-newastro@yahoogroups.com, "Wodaski - Yahoo" <yahoo@w...>
              wrote:
              > A bright, offset circle like that usually indicates that, at the
              time the
              > flats were taken, there was some back illumination from the
              focuser/camera
              > end of things. This causes a reflection off of some dust (fairly
              far from
              > the camera in this case because it is so large), leaving a bright
              spot when
              > the flat is applied.
              >
              > This typically occurs either when flats are taken in daylight or
              dusk
              > conditions, or any time the light source can enter the back end of
              the
              > scope.


              I've had the same problem as Ron described. I cured it by wrapping
              things with aluminum foil in the back when I shot my flats (avoiding
              covering the cooling ports for the cameras). One handy way to be
              assured your flats are free of such spurious light is to shoot a dark
              of 5-10 seconds with the aperture cover on. If you see things that
              should not be there, you have some light leaking from someplace.

              I always shoot a few darks like that before starting my flats. If I
              can't get a clean dark that way, I keep adding or adjusting the
              aluminum foil until I do. If the darks suffer from light ingress, you
              will never get a decent flat if you are shooting them during twilight
              (evening or morning)

              Richard
            • mike_from_tn@yahoo.com
              Thanks for all the suggestions! Actually I am very methodic about flats and have wrapped the camera and drawtube with cloth for some time now. What is
              Message 6 of 10 , Feb 2, 2004
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                Thanks for all the suggestions!

                Actually I am very methodic about flats and have wrapped the camera
                and drawtube with cloth for some time now. What is perplexing this
                time around is that this effect seems to only happen with the
                Schuler Ir blocking luminance filter. I note the artifact is present
                both in the luminance flats as well as the luminance image frame. I
                also took RGB filtered shots of the same object and neither the flat
                frames nor the object frames had the artifact present. The filter is
                spotless so perhaps I am dealing with a reflection issue?

                It almost seems as if the flat field is correcting too strongly or
                perhaps not enough. Guess I'll go back to shooting with the SBIG
                clear that didn't exhibit any of the odd effects.

                Mike
              • Wodaski - Yahoo
                A strong possibility: you have an IR source that is reflecting off of that filter. Ron Wodaski The New CCD Astronomy Book web site: http://www.newastro.com ...
                Message 7 of 10 , Feb 2, 2004
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                  A strong possibility: you have an IR source that is reflecting off of that
                  filter.


                  Ron Wodaski
                  The New CCD Astronomy Book
                  web site: http://www.newastro.com


                  -----Original Message-----
                  From: mike_from_tn@... [mailto:mike_from_tn@...]
                  Sent: Monday, February 02, 2004 8:25 AM
                  To: ccd-newastro@yahoogroups.com
                  Subject: [ccd-newastro] Re: What the heck....a donut near M81?

                  Thanks for all the suggestions!

                  Actually I am very methodic about flats and have wrapped the camera
                  and drawtube with cloth for some time now. What is perplexing this
                  time around is that this effect seems to only happen with the
                  Schuler Ir blocking luminance filter. I note the artifact is present
                  both in the luminance flats as well as the luminance image frame. I
                  also took RGB filtered shots of the same object and neither the flat
                  frames nor the object frames had the artifact present. The filter is
                  spotless so perhaps I am dealing with a reflection issue?

                  It almost seems as if the flat field is correcting too strongly or
                  perhaps not enough. Guess I'll go back to shooting with the SBIG
                  clear that didn't exhibit any of the odd effects.

                  Mike







                  Yahoo! Groups Links

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                • rdcrisp
                  ... of that ... Just try shooting a 10 sec light with the aperture covered and everything else covered up as you normally do. Do it with light outside and see
                  Message 8 of 10 , Feb 2, 2004
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                    --- In ccd-newastro@yahoogroups.com, "Wodaski - Yahoo" <yahoo@w...>
                    wrote:
                    > A strong possibility: you have an IR source that is reflecting off
                    of that
                    > filter.


                    Just try shooting a 10 sec light with the aperture covered and
                    everything else covered up as you normally do. Do it with light
                    outside and see if you have any leaks. If that "dark" doesn't look
                    clean, you will never have a good flat.

                    Richard
                  • mike_from_tn@yahoo.com
                    I did the light leak test last night with a 500watt halogen worklight near the scope and all is well. Looks like a dark frame. The artifact while present in
                    Message 9 of 10 , Feb 2, 2004
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                      I did the light leak test last night with a 500watt halogen
                      worklight near the scope and all is well. Looks like a dark frame.
                      The artifact while present in the Ir filtered object and flat frames
                      is non-existent with the SBIG RGB filters. Ron mentioned an Ir
                      source reflecting off the Ir filter and I cannot think of any unless
                      the LED in the CFW is on all the time but wouldn't this fog my
                      images?. I purposefully stay away from anodized parts due to the Ir
                      issue. My focusers and extension tubes are painted on the inside
                      with Krylon ultra flat black. I am going to machine another drawtube
                      and use flocking paper on the inside and see if that has an effect.
                      This scope seems well made for imaging as far as baffles go- Its got
                      a CO of 50%! Seems to work pretty well though judging from Cord
                      Scholz' images. I am looking forward to getting this issue worked
                      out so I can concentrate on imaging again. For nor I am going to put
                      the Shuler filter back on the shelf.

                      Here is a frame made with the same scope and camera setup however
                      the SBIG clear was used.

                      http://personalpages.tds.net/~mfleenor/st10/m51_30min_mk69_fullresolu
                      tion.jpg

                      Mike



                      > Just try shooting a 10 sec light with the aperture covered and
                      > everything else covered up as you normally do. Do it with light
                      > outside and see if you have any leaks. If that "dark" doesn't look
                      > clean, you will never have a good flat.
                      >
                      > Richard
                    • rdcrisp
                      ... Not to belabor the point, but you did shoot the dark as a covered aperture light frame right? If you told it to shoot a dark, then the shutter would not
                      Message 10 of 10 , Feb 2, 2004
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                        --- In ccd-newastro@yahoogroups.com, mike_from_tn@y... wrote:
                        > I did the light leak test last night with a 500watt halogen
                        > worklight near the scope and all is well. Looks like a dark frame.
                        > The artifact while present in the Ir filtered object and flat

                        Not to belabor the point, but you did shoot the dark as a "covered
                        aperture light frame" right? If you told it to shoot a dark, then the
                        shutter would not open. The shutter needs to be open to be a
                        meaningful test.

                        Richard
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