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RE: [ccd-newastro] Flat fields with the ST-237

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  • Ron Wodaski
    I looked at the flat fields; they do look a bit odd, with those lines through them. I wonder if that is an artifact of the light box somehow? One doesn t
    Message 1 of 28 , Dec 3, 2000
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      I looked at the flat fields; they do look a bit odd, with those lines
      through them. I wonder if that is an artifact of the light box somehow? One
      doesn't expect to see lines like that in a normal flat field.

      HOWEVER: I see a similar pattern in my own flat fields with the Megrez 80,
      and I plan to do some experiments to see why this is so. Here's a look at
      one of my ST-237 flat fields:

      http://www.wodaski.com/wodaski/images/ST_237/flat_AVG.jpg

      In answer to your questions: see below.

      Ron Wodaski
      The New Astronomy Book Site - http://www.newastro.com



      -----Original Message-----
      From: KSBTK@HOME [mailto:ksbtk@...]
      Sent: Sunday, December 03, 2000 6:49 AM
      To: ccd-newastro@egroups.com
      Subject: [ccd-newastro] Flat fields with the ST-237

      1. Is it best to achieve approximately the same value for each flat taken
      through a colored filter? As I mentioned above, I varied the exposure
      length to achieve a value of approximately 1600 for the RGB images.

      --> Yes. But they can vary within the norms for a flat field, as you can
      (and should) take steps to normalize your background levels in the RGB
      images before you combine them anyone. Typically, you simply subtract from
      the background to get them all in the same range (I use 50 units for the
      background with the ST-7/8; I might drop that to 25 for the ST-237).

      2. I took 5 each of the RGB flats. Ron, your chapter on flat fields
      mentions median combining each of the flats taken for a particular color
      filter, prior to image calibaration. Do you then median combine the
      already-combined RGB flats or do you subrtract them from the images
      individually?

      --> Every image is calibrated (bias, dark, flat-field) individually.

      3. Is it necessary, or desirable, to do a dark field subtraction from the
      flat fields prior to the median combine?


      --> Yes, the flat field itself must be calibrated prior to use, so each of
      its individual images have to be calibrated with a dark frame.
    • Ivor Barker
      Hi Kevin, What F/R were you using? 3.3? I think your flats could do with longer exposure times, it appears that you have a bright spot in the center. I have
      Message 2 of 28 , Dec 3, 2000
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        Hi Kevin,

        What F/R were you using? 3.3?
        I think your flats could do with longer exposure times, it appears that you have a bright spot in the center.
        I have uploaded one of my flats, see what  you think.

        --
        Ivor
        At 12:50 AM 12/4/2000 +0000, you wrote:
        Good evening:

        I have uploaded jpeg images of my flat fields for anyone who would
        like to examine/comment on them.

        Clear skies,
        Kevin
        ksbtk@...



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        --
         Ivor Barker
        10" LX 200
        ST-237
        37 08 24 N
        121 36 25 W
        Please take a look at my Messier Project (updated daily - almost)
      • Ivor Barker
        Hi Kevin, Looks like you need a bit more exposure, also the center seems too light, I have just uploaded a f/3.75 flat. Cheers !! --Ivor ... -- Ivor Barker 10
        Message 3 of 28 , Dec 3, 2000
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          Hi Kevin,

          Looks like you need a bit more exposure, also the center seems too light, I have just uploaded a f/3.75 flat.

          Cheers !!
          --Ivor
          At 12:50 AM 12/4/2000 +0000, you wrote:
          Good evening:

          I have uploaded jpeg images of my flat fields for anyone who would
          like to examine/comment on them.

          Clear skies,
          Kevin
          ksbtk@...



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          --
           Ivor Barker
          10" LX 200
          ST-237
          37 08 24 N
          121 36 25 W
          Please take a look at my Messier Project (updated daily - almost)
        • Kevin Dixon
          Good afternoon Ron: Thanks for your response. With your indulgence, I have a few more questions. ... Was this taken with the ST-237 in Fastar mode? The
          Message 4 of 28 , Dec 4, 2000
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            Good afternoon Ron:

            Thanks for your response. With your indulgence, I have a few more
            questions.

            >Here's a look at
            > one of my ST-237 flat fields:

            Was this taken with the ST-237 in Fastar mode? The reason I ask is
            because Fred Herman told me to put the dew shield on the C8 and set
            the lite box on top of the dew shield. That generated the images
            that I downloaded yesterday.

            For the heck of it, I also set the lite box directly on the ST-237
            while in Fastar mode. I'll download that image if you could please
            take a look at it. I'll put it in the same folder in the files. It
            is drastically different from the images when using the dew shield.

            BTW, I have seen the pattern of lines that are in the flat fields in
            some of the raw images I have taken with the ST-237 in fastar mode.

            Am I correct in assuming that the proof is in the pudding <g>? In
            other words, if I subtract the flat fields from the raw images and
            they look okay, does that mean the flats are acceptable?

            Please see one additional question below.

            > --> Yes. But they can vary within the norms for a flat field, as
            you can
            > (and should) take steps to normalize your background levels in the
            RGB
            > images before you combine them anyone. Typically, you simply
            subtract from
            > the background to get them all in the same range (I use 50 units
            for the
            > background with the ST-7/8; I might drop that to 25 for the ST-237).

            You lost me here, due to my lack of understanding of calibration
            fundamentals. Can you elaborate on normalizing background levels and
            how this is done. Do you mean to conduct the calibration and
            determine if the background levels are similar? What do you do if
            they are not? Do you simply subtract again? This is complex stuff
            but I sincerely appreciate your help with it. CAN'T WAIT FOR THE
            BOOK!

            Clear skies,
            Kevin
            ksbtk@...
          • Ron Wodaski
            Yes: the bottom line is in how effective the flat field is. No matter how weird it looks, if you get an even average background value, you have a good flat
            Message 5 of 28 , Dec 4, 2000
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              Yes: the bottom line is in how effective the flat field is. No matter how
              weird it looks, if you get an even average background value, you have a good
              flat field. It took me about a year to really nail it down. And I'm still
              fighting with certain aspects of getting an even field. <g>

              Ron Wodaski
              The New Astronomy Book Site - http://www.newastro.com



              -----Original Message-----
              From: Kevin Dixon [mailto:ksbtk@...]
              Sent: Monday, December 04, 2000 12:40 PM
              To: ccd-newastro@egroups.com
              Subject: [ccd-newastro] Re: Flat fields with the ST-237


              Good afternoon Ron:

              Thanks for your response. With your indulgence, I have a few more
              questions.

              >Here's a look at
              > one of my ST-237 flat fields:

              Was this taken with the ST-237 in Fastar mode? The reason I ask is
              because Fred Herman told me to put the dew shield on the C8 and set
              the lite box on top of the dew shield. That generated the images
              that I downloaded yesterday.

              For the heck of it, I also set the lite box directly on the ST-237
              while in Fastar mode. I'll download that image if you could please
              take a look at it. I'll put it in the same folder in the files. It
              is drastically different from the images when using the dew shield.

              BTW, I have seen the pattern of lines that are in the flat fields in
              some of the raw images I have taken with the ST-237 in fastar mode.

              Am I correct in assuming that the proof is in the pudding <g>? In
              other words, if I subtract the flat fields from the raw images and
              they look okay, does that mean the flats are acceptable?

              Please see one additional question below.

              > --> Yes. But they can vary within the norms for a flat field, as
              you can
              > (and should) take steps to normalize your background levels in the
              RGB
              > images before you combine them anyone. Typically, you simply
              subtract from
              > the background to get them all in the same range (I use 50 units
              for the
              > background with the ST-7/8; I might drop that to 25 for the ST-237).

              You lost me here, due to my lack of understanding of calibration
              fundamentals. Can you elaborate on normalizing background levels and
              how this is done. Do you mean to conduct the calibration and
              determine if the background levels are similar? What do you do if
              they are not? Do you simply subtract again? This is complex stuff
              but I sincerely appreciate your help with it. CAN'T WAIT FOR THE
              BOOK!

              Clear skies,
              Kevin
              ksbtk@...





              To unsubscribe from this group, send an email to:
              ccd-newastro-unsubscribe@egroups.com
            • Kevin Dixon
              Hi Ivor: I was using the ST-237 in fastar mode so I was at a focal ratio of 1.95. Keep in mind this means that the camera is on the front end of my SCT, where
              Message 6 of 28 , Dec 4, 2000
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                Hi Ivor:

                I was using the ST-237 in fastar mode so I was at a focal ratio of
                1.95. Keep in mind this means that the camera is on the front end of
                my SCT, where the secondary mirror normally is. This presents a bit
                of a unique situation in regards to creating flat fields with the
                litebox.

                > I think your flats could do with longer exposure times, it appears
                that you have a bright spot in the center.

                When I went to longer exposure times, I exceeded the 2000 unit
                guideline that Ron recommended.

                > I have uploaded one of my flats, see what you think.

                If I get a chance tonite, I will set my SCT up in a similar mode as
                you and see how the flat fields compare.

                Thanks for you help with this.

                Clear skies,
                Kevin
                ksbtk@...
              • Ron Wodaski
                Another point about flat fields: if you are using a chip with antiblooming (this includes the 237), then it is even more important to stay below the 50%
                Message 7 of 28 , Dec 4, 2000
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                  Another point about flat fields: if you are using a chip with antiblooming
                  (this includes the 237), then it is even more important to stay below the
                  50% threshold. ABG chips are non-linear past the 50% point, and a flat
                  field, to properly equalize your image, must have linear data. That is, a
                  point that is 10% brighter in reality MUST be 10% brighter in the flat
                  field. If the flat field is too bright, this relationship will be lost, and
                  the flat field will be ineffective.

                  Fortunately, the ST-237 does not have aggressive ABG settings; the chip does
                  remain linear a bit above the 50% line. This was probably done in the design
                  because of the 12-bit data stream -- 50% of 4096 was seen as too low. With
                  65,000 values, 50% is seen as safer (better control of blooming with a lower
                  changeover point).

                  Ron Wodaski
                  The New Astronomy Book Site - http://www.newastro.com



                  -----Original Message-----
                  From: Kevin Dixon [mailto:ksbtk@...]
                  Sent: Monday, December 04, 2000 1:27 PM
                  To: ccd-newastro@egroups.com
                  Subject: [ccd-newastro] Re: Flat fields with the ST-237


                  Hi Ivor:

                  I was using the ST-237 in fastar mode so I was at a focal ratio of
                  1.95. Keep in mind this means that the camera is on the front end of
                  my SCT, where the secondary mirror normally is. This presents a bit
                  of a unique situation in regards to creating flat fields with the
                  litebox.

                  > I think your flats could do with longer exposure times, it appears
                  that you have a bright spot in the center.

                  When I went to longer exposure times, I exceeded the 2000 unit
                  guideline that Ron recommended.

                  > I have uploaded one of my flats, see what you think.

                  If I get a chance tonite, I will set my SCT up in a similar mode as
                  you and see how the flat fields compare.

                  Thanks for you help with this.

                  Clear skies,
                  Kevin
                  ksbtk@...





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                • KSBTK@HOME
                  Ron: If I were to download an image of M51 and the corresponding dark and flat fields, could you play with them to see if you think the flat field is
                  Message 8 of 28 , Dec 4, 2000
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                    Ron:

                    If I were to download an image of M51 and the corresponding dark and flat
                    fields, could you play with them to see if you think the flat field is
                    effective? I'll wait to hear from you before downloading. Thanks.

                    Clear skies,
                    Kevin
                    ksbtk@...

                    From: "Ron Wodaski" <ronw@...>

                    > Yes: the bottom line is in how effective the flat field is. No matter how
                    > weird it looks, if you get an even average background value, you have a
                    good
                    > flat field. It took me about a year to really nail it down. And I'm still
                    > fighting with certain aspects of getting an even field. <g>
                  • KSBTK@HOME
                    Ron: Understood - I ll try several experiments this week including using the ST-237 through the C8 D and then imaging a sparse open cluster. Any suggestions
                    Message 9 of 28 , Dec 4, 2000
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                      Ron:

                      Understood - I'll try several experiments this week including using the
                      ST-237 through the C8 D and then imaging a sparse open cluster. Any
                      suggestions as to a good cluster of this type for this time of year?

                      Also, did you creat flat fields with the ST-237 while in fastar mode? I'd
                      be interested to see what they look like.

                      I will download the images into the feedback file folder. I will include
                      images of the horsehead as well in case this would be more useful than the
                      M51 image. They should be available soon. Again, many thanks for all your
                      help.

                      Clear skies,
                      Kevin
                      ksbtk@...

                      From: "Ron Wodaski" <ronw@...>


                      > Sure. But what you are looking for is the lack of a radial gradient (that
                      > is, the central bright spot). You may still have a linear gradient (light
                      > pollution induced, usually, and brighter on one side or the other); a flat
                      > field doesn't fix that, just the brightness variations in your optical
                      > setup.
                      >
                      > So if you have a bright, extended object in the center of the frame, you
                      > can't really evaluate a flat field with that. An image of a random star
                      > field is far better, or an image of sparse open cluster.
                    • KSBTK@HOME
                      Ron: I have just finished uploading 10 files into the Feedback folder in a folder entitled ST237 images, dark and flat fields. These include single RGB
                      Message 10 of 28 , Dec 4, 2000
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                        Ron:

                        I have just finished uploading 10 files into the Feedback folder in a folder
                        entitled "ST237 images, dark and flat fields. These include single RGB
                        images of the horsehead, M51, a dark frame and the RGB flat fields.

                        It'll be most interesting to see what your evaluation yields.

                        BTW, any other comments about the raw images are most welcomed.

                        Again, infinite thanks.

                        Clear skies,
                        Kevin
                        ksbtk@...

                        From: "Ron Wodaski" <ronw@...>

                        > Sure. But what you are looking for is the lack of a radial gradient (that
                        > is, the central bright spot). You may still have a linear gradient (light
                        > pollution induced, usually, and brighter on one side or the other); a flat
                        > field doesn't fix that, just the brightness variations in your optical
                        > setup.
                        >
                        > So if you have a bright, extended object in the center of the frame, you
                        > can't really evaluate a flat field with that. An image of a random star
                        > field is far better, or an image of sparse open cluster.
                      • Ron Wodaski
                        Sure. But what you are looking for is the lack of a radial gradient (that is, the central bright spot). You may still have a linear gradient (light pollution
                        Message 11 of 28 , Dec 4, 2000
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                          Sure. But what you are looking for is the lack of a radial gradient (that
                          is, the central bright spot). You may still have a linear gradient (light
                          pollution induced, usually, and brighter on one side or the other); a flat
                          field doesn't fix that, just the brightness variations in your optical
                          setup.

                          So if you have a bright, extended object in the center of the frame, you
                          can't really evaluate a flat field with that. An image of a random star
                          field is far better, or an image of sparse open cluster.

                          Ron Wodaski
                          The New Astronomy Book Site - http://www.newastro.com



                          -----Original Message-----
                          From: KSBTK@HOME [mailto:ksbtk@...]
                          Sent: Monday, December 04, 2000 2:15 PM
                          To: ccd-newastro@egroups.com
                          Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                          Ron:

                          If I were to download an image of M51 and the corresponding dark and flat
                          fields, could you play with them to see if you think the flat field is
                          effective? I'll wait to hear from you before downloading. Thanks.

                          Clear skies,
                          Kevin
                          ksbtk@...

                          From: "Ron Wodaski" <ronw@...>

                          > Yes: the bottom line is in how effective the flat field is. No matter how
                          > weird it looks, if you get an even average background value, you have a
                          good
                          > flat field. It took me about a year to really nail it down. And I'm still
                          > fighting with certain aspects of getting an even field. <g>





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                          ccd-newastro-unsubscribe@egroups.com
                        • Ron Wodaski
                          There is a Fastar flat field sample on this page, about half way down: http://www.wodaski.com/wodaski/review_fastar.htm I recently took images of M34 and M38;
                          Message 12 of 28 , Dec 4, 2000
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                            There is a Fastar flat field sample on this page, about half way down:

                            http://www.wodaski.com/wodaski/review_fastar.htm

                            I recently took images of M34 and M38; both are relatively open. M34 is the
                            more sparse. But just about any random star field outside of the Milky Way
                            will do the job. if it is near the zenith and in the darkest portion of your
                            sky, even better; fewer light pollution issues to deal with.

                            Ron Wodaski
                            The New Astronomy Book Site - http://www.newastro.com



                            -----Original Message-----
                            From: KSBTK@HOME [mailto:ksbtk@...]
                            Sent: Monday, December 04, 2000 2:59 PM
                            To: ccd-newastro@egroups.com
                            Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                            Ron:

                            Understood - I'll try several experiments this week including using the
                            ST-237 through the C8 D and then imaging a sparse open cluster. Any
                            suggestions as to a good cluster of this type for this time of year?

                            Also, did you creat flat fields with the ST-237 while in fastar mode? I'd
                            be interested to see what they look like.

                            I will download the images into the feedback file folder. I will include
                            images of the horsehead as well in case this would be more useful than the
                            M51 image. They should be available soon. Again, many thanks for all your
                            help.

                            Clear skies,
                            Kevin
                            ksbtk@...

                            From: "Ron Wodaski" <ronw@...>


                            > Sure. But what you are looking for is the lack of a radial gradient (that
                            > is, the central bright spot). You may still have a linear gradient (light
                            > pollution induced, usually, and brighter on one side or the other); a flat
                            > field doesn't fix that, just the brightness variations in your optical
                            > setup.
                            >
                            > So if you have a bright, extended object in the center of the frame, you
                            > can't really evaluate a flat field with that. An image of a random star
                            > field is far better, or an image of sparse open cluster.





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                          • Ivor Barker
                            Yes Kevin, let me know it will be interesting to see what the comparison is. I have just arrived in Las Vegas, so my emails may be a bit erratic until
                            Message 13 of 28 , Dec 5, 2000
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                              Yes Kevin, let me know it will be interesting to see what the comparison is.

                              I have just arrived in Las Vegas, so my emails may be a bit erratic until Thursday.

                              Cheers !!
                              --Ivor
                              --
                               Ivor Barker
                              10" LX 200
                              ST-237
                              37 08 24 N
                              121 36 25 W
                              http://www.employees.org/~ibarker/Astronomy
                              Please take a look at my Messier Project (updated daily - almost)
                              http://www.employees.org/~ibarker/Astronomy/Messier.html


                              At 09:27 PM 12/4/2000 +0000, you wrote:
                              Hi Ivor:

                              I was using the ST-237 in fastar mode so I was at a focal ratio of
                              1.95.  Keep in mind this means that the camera is on the front end of
                              my SCT, where the secondary mirror normally is.  This presents a bit
                              of a unique situation in regards to creating flat fields with the
                              litebox.

                              > I think your flats could do with longer exposure times, it appears
                              that you have a bright spot in the center.

                              When I went to longer exposure times, I exceeded the 2000 unit
                              guideline that Ron recommended.

                              > I have uploaded one of my flats, see what  you think.

                              If I get a chance tonite, I will set my SCT up in a similar mode as
                              you and see how the flat fields compare.

                              Thanks for you help with this.

                              Clear skies,
                              Kevin
                              ksbtk@...




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                            • KSBTK@HOME
                              Good evening Ron: Have you gotten an opportunity to work with the images that I uploaded yet? I played around with them a bit and I think the flats are going
                              Message 14 of 28 , Dec 5, 2000
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                                Good evening Ron:

                                Have you gotten an opportunity to work with the images that I uploaded yet?
                                I played around with them a bit and I think the flats are going to work
                                correctly. Of course, this is a "newbie" opinion.

                                I was going to try to image M34 tonite and create more flats but the wind
                                chill factor is about 10 degrees and the wind is gusting up to 30 mph so I
                                don't think the telescope will be very steady. I'll have to try again
                                tomorrow night instead.

                                Looking forward to your comments.

                                Clear skies,
                                Kevin
                                ksbtk@...

                                From: "Ron Wodaski" <ronw@...>

                                > Sure. But what you are looking for is the lack of a radial gradient (that
                                > is, the central bright spot). You may still have a linear gradient (light
                                > pollution induced, usually, and brighter on one side or the other); a flat
                                > field doesn't fix that, just the brightness variations in your optical
                                > setup.
                                >
                                > So if you have a bright, extended object in the center of the frame, you
                                > can't really evaluate a flat field with that. An image of a random star
                                > field is far better, or an image of sparse open cluster.
                                >
                                > Ron Wodaski
                                > The New Astronomy Book Site - http://www.newastro.com
                                >
                                >
                                >
                                > -----Original Message-----
                                > From: KSBTK@HOME [mailto:ksbtk@...]
                                > Sent: Monday, December 04, 2000 2:15 PM
                                > To: ccd-newastro@egroups.com
                                > Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237
                                >
                                >
                                > Ron:
                                >
                                > If I were to download an image of M51 and the corresponding dark and flat
                                > fields, could you play with them to see if you think the flat field is
                                > effective? I'll wait to hear from you before downloading. Thanks.
                                >
                                > Clear skies,
                                > Kevin
                                > ksbtk@...
                              • Ron Wodaski
                                Not yet; hopefully this evening. Had some emergency surgery to do on the ATWB site. Ron Wodaski The New Astronomy Book Site - http://www.newastro.com ... From:
                                Message 15 of 28 , Dec 5, 2000
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                                  Not yet; hopefully this evening. Had some emergency surgery to do on the
                                  ATWB site.

                                  Ron Wodaski
                                  The New Astronomy Book Site - http://www.newastro.com



                                  -----Original Message-----
                                  From: KSBTK@HOME [mailto:ksbtk@...]
                                  Sent: Tuesday, December 05, 2000 2:59 PM
                                  To: ccd-newastro@egroups.com
                                  Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                  Good evening Ron:

                                  Have you gotten an opportunity to work with the images that I uploaded yet?
                                  I played around with them a bit and I think the flats are going to work
                                  correctly. Of course, this is a "newbie" opinion.

                                  I was going to try to image M34 tonite and create more flats but the wind
                                  chill factor is about 10 degrees and the wind is gusting up to 30 mph so I
                                  don't think the telescope will be very steady. I'll have to try again
                                  tomorrow night instead.

                                  Looking forward to your comments.

                                  Clear skies,
                                  Kevin
                                  ksbtk@...

                                  From: "Ron Wodaski" <ronw@...>

                                  > Sure. But what you are looking for is the lack of a radial gradient (that
                                  > is, the central bright spot). You may still have a linear gradient (light
                                  > pollution induced, usually, and brighter on one side or the other); a flat
                                  > field doesn't fix that, just the brightness variations in your optical
                                  > setup.
                                  >
                                  > So if you have a bright, extended object in the center of the frame, you
                                  > can't really evaluate a flat field with that. An image of a random star
                                  > field is far better, or an image of sparse open cluster.
                                  >
                                  > Ron Wodaski
                                  > The New Astronomy Book Site - http://www.newastro.com
                                  >
                                  >
                                  >
                                  > -----Original Message-----
                                  > From: KSBTK@HOME [mailto:ksbtk@...]
                                  > Sent: Monday, December 04, 2000 2:15 PM
                                  > To: ccd-newastro@egroups.com
                                  > Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237
                                  >
                                  >
                                  > Ron:
                                  >
                                  > If I were to download an image of M51 and the corresponding dark and flat
                                  > fields, could you play with them to see if you think the flat field is
                                  > effective? I'll wait to hear from you before downloading. Thanks.
                                  >
                                  > Clear skies,
                                  > Kevin
                                  > ksbtk@...





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                                • Ron Wodaski
                                  I m downloading your images now; will have critique later today. I ve been unexpectedly occupied; I had a mount arrive for review/testing that is a prototype
                                  Message 16 of 28 , Dec 7, 2000
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                                    I'm downloading your images now; will have critique later today.

                                    I've been unexpectedly occupied; I had a mount arrive for review/testing
                                    that is a prototype that a lot of folks will be interested in (G-11 with
                                    Gemini goto). So far, have only used it in visual testing scenarios.

                                    Ron Wodaski
                                    The New Astronomy Book Site - http://www.newastro.com



                                    -----Original Message-----
                                    From: KSBTK@HOME [mailto:ksbtk@...]
                                    Sent: Tuesday, December 05, 2000 2:59 PM
                                    To: ccd-newastro@egroups.com
                                    Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                    Good evening Ron:

                                    Have you gotten an opportunity to work with the images that I uploaded yet?
                                    I played around with them a bit and I think the flats are going to work
                                    correctly. Of course, this is a "newbie" opinion.

                                    I was going to try to image M34 tonite and create more flats but the wind
                                    chill factor is about 10 degrees and the wind is gusting up to 30 mph so I
                                    don't think the telescope will be very steady. I'll have to try again
                                    tomorrow night instead.

                                    Looking forward to your comments.

                                    Clear skies,
                                    Kevin
                                    ksbtk@...

                                    From: "Ron Wodaski" <ronw@...>

                                    > Sure. But what you are looking for is the lack of a radial gradient (that
                                    > is, the central bright spot). You may still have a linear gradient (light
                                    > pollution induced, usually, and brighter on one side or the other); a flat
                                    > field doesn't fix that, just the brightness variations in your optical
                                    > setup.
                                    >
                                    > So if you have a bright, extended object in the center of the frame, you
                                    > can't really evaluate a flat field with that. An image of a random star
                                    > field is far better, or an image of sparse open cluster.
                                    >
                                    > Ron Wodaski
                                    > The New Astronomy Book Site - http://www.newastro.com
                                    >
                                    >
                                    >
                                    > -----Original Message-----
                                    > From: KSBTK@HOME [mailto:ksbtk@...]
                                    > Sent: Monday, December 04, 2000 2:15 PM
                                    > To: ccd-newastro@egroups.com
                                    > Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237
                                    >
                                    >
                                    > Ron:
                                    >
                                    > If I were to download an image of M51 and the corresponding dark and flat
                                    > fields, could you play with them to see if you think the flat field is
                                    > effective? I'll wait to hear from you before downloading. Thanks.
                                    >
                                    > Clear skies,
                                    > Kevin
                                    > ksbtk@...





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                                    ccd-newastro-unsubscribe@egroups.com
                                  • KSBTK@HOME
                                    Thanks Ron - I sincerely appreciate it. I am extremely interested in your evaluation of the G-11 with goto. Do you expect this to improve the tracking
                                    Message 17 of 28 , Dec 7, 2000
                                    • 0 Attachment
                                      Thanks Ron - I sincerely appreciate it.

                                      I am extremely interested in your evaluation of the G-11 with goto. Do you
                                      expect this to improve the tracking capability of the mount, particularly
                                      with respect to CCD imaging? What scope are you using with the mount? The
                                      FSQ-106 by chance?

                                      Clear skies,
                                      Kevin
                                      ksbtk@...

                                      From: "Ron Wodaski" <ronw@...>

                                      > I'm downloading your images now; will have critique later today.
                                      >
                                      > I've been unexpectedly occupied; I had a mount arrive for review/testing
                                      > that is a prototype that a lot of folks will be interested in (G-11 with
                                      > Gemini goto). So far, have only used it in visual testing scenarios.
                                    • Ron Wodaski
                                      The goto version uses server motors, not the Hurst steppers that have been problematic for some. I tested last night for visual only -- no real polar
                                      Message 18 of 28 , Dec 7, 2000
                                      • 0 Attachment
                                        The goto version uses server motors, not the Hurst steppers that have been
                                        problematic for some. I tested last night for visual only -- no real polar
                                        alignment, just sighted Polaris through the borehole. I got really good
                                        pointing accuracy, could have put objects on an ST-7E chip in the FSQ-106.

                                        I had the FSQ-106 on it, with the Megrez piggy-backed to add some weight to
                                        really test it out. I will image with it on the next clear night. So far, my
                                        experiences have been pretty positive.

                                        Ron Wodaski
                                        The New Astronomy Book Site - http://www.newastro.com



                                        -----Original Message-----
                                        From: KSBTK@HOME [mailto:ksbtk@...]
                                        Sent: Thursday, December 07, 2000 3:00 PM
                                        To: ccd-newastro@egroups.com
                                        Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                        Thanks Ron - I sincerely appreciate it.

                                        I am extremely interested in your evaluation of the G-11 with goto. Do you
                                        expect this to improve the tracking capability of the mount, particularly
                                        with respect to CCD imaging? What scope are you using with the mount? The
                                        FSQ-106 by chance?

                                        Clear skies,
                                        Kevin
                                        ksbtk@...

                                        From: "Ron Wodaski" <ronw@...>

                                        > I'm downloading your images now; will have critique later today.
                                        >
                                        > I've been unexpectedly occupied; I had a mount arrive for review/testing
                                        > that is a prototype that a lot of folks will be interested in (G-11 with
                                        > Gemini goto). So far, have only used it in visual testing scenarios.





                                        To unsubscribe from this group, send an email to:
                                        ccd-newastro-unsubscribe@egroups.com
                                      • Ron Wodaski
                                        Make that servo motors. Ron Wodaski The New Astronomy Book Site - http://www.newastro.com ... From: Ron Wodaski [mailto:ronw@nwlink.com] Sent: Thursday,
                                        Message 19 of 28 , Dec 7, 2000
                                        • 0 Attachment
                                          Make that "servo" motors. <g>

                                          Ron Wodaski
                                          The New Astronomy Book Site - http://www.newastro.com



                                          -----Original Message-----
                                          From: Ron Wodaski [mailto:ronw@...]
                                          Sent: Thursday, December 07, 2000 3:27 PM
                                          To: ccd-newastro@egroups.com
                                          Subject: RE: [ccd-newastro] Re: Flat fields with the ST-237


                                          The goto version uses server motors, not the Hurst steppers that have been
                                          problematic for some. I tested last night for visual only -- no real polar
                                          alignment, just sighted Polaris through the borehole. I got really good
                                          pointing accuracy, could have put objects on an ST-7E chip in the FSQ-106.

                                          I had the FSQ-106 on it, with the Megrez piggy-backed to add some weight to
                                          really test it out. I will image with it on the next clear night. So far, my
                                          experiences have been pretty positive.

                                          Ron Wodaski
                                          The New Astronomy Book Site - http://www.newastro.com



                                          -----Original Message-----
                                          From: KSBTK@HOME [mailto:ksbtk@...]
                                          Sent: Thursday, December 07, 2000 3:00 PM
                                          To: ccd-newastro@egroups.com
                                          Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                          Thanks Ron - I sincerely appreciate it.

                                          I am extremely interested in your evaluation of the G-11 with goto. Do you
                                          expect this to improve the tracking capability of the mount, particularly
                                          with respect to CCD imaging? What scope are you using with the mount? The
                                          FSQ-106 by chance?

                                          Clear skies,
                                          Kevin
                                          ksbtk@...

                                          From: "Ron Wodaski" <ronw@...>

                                          > I'm downloading your images now; will have critique later today.
                                          >
                                          > I've been unexpectedly occupied; I had a mount arrive for review/testing
                                          > that is a prototype that a lot of folks will be interested in (G-11 with
                                          > Gemini goto). So far, have only used it in visual testing scenarios.





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






                                          To unsubscribe from this group, send an email to:
                                          ccd-newastro-unsubscribe@egroups.com
                                        • KSBTK@HOME
                                          Ron - if I may be so bold - when you do image with the FSQ-106, could you please acquire some images with the ST-237. This is a combination that I may add to
                                          Message 20 of 28 , Dec 7, 2000
                                          • 0 Attachment
                                            Ron - if I may be so bold - when you do image with the FSQ-106, could you
                                            please acquire some images with the ST-237. This is a combination that I
                                            may add to my wish list, pending your review.

                                            Clear skies,
                                            Kevin
                                            ksbtk@...

                                            ----- Original Message -----
                                            From: "Ron Wodaski" <ronw@...>
                                            To: <ccd-newastro@egroups.com>
                                            Sent: Thursday, December 07, 2000 6:27 PM
                                            Subject: RE: [ccd-newastro] Re: Flat fields with the ST-237


                                            > The goto version uses server motors, not the Hurst steppers that have been
                                            > problematic for some. I tested last night for visual only -- no real polar
                                            > alignment, just sighted Polaris through the borehole. I got really good
                                            > pointing accuracy, could have put objects on an ST-7E chip in the FSQ-106.
                                            >
                                            > I had the FSQ-106 on it, with the Megrez piggy-backed to add some weight
                                            to
                                            > really test it out. I will image with it on the next clear night. So far,
                                            my
                                            > experiences have been pretty positive.
                                            >
                                            > Ron Wodaski
                                            > The New Astronomy Book Site - http://www.newastro.com
                                            >
                                            >
                                            >
                                            > -----Original Message-----
                                            > From: KSBTK@HOME [mailto:ksbtk@...]
                                            > Sent: Thursday, December 07, 2000 3:00 PM
                                            > To: ccd-newastro@egroups.com
                                            > Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237
                                            >
                                            >
                                            > Thanks Ron - I sincerely appreciate it.
                                            >
                                            > I am extremely interested in your evaluation of the G-11 with goto. Do
                                            you
                                            > expect this to improve the tracking capability of the mount, particularly
                                            > with respect to CCD imaging? What scope are you using with the mount?
                                            The
                                            > FSQ-106 by chance?
                                            >
                                            > Clear skies,
                                            > Kevin
                                            > ksbtk@...
                                            >
                                            > From: "Ron Wodaski" <ronw@...>
                                            >
                                            > > I'm downloading your images now; will have critique later today.
                                            > >
                                            > > I've been unexpectedly occupied; I had a mount arrive for review/testing
                                            > > that is a prototype that a lot of folks will be interested in (G-11 with
                                            > > Gemini goto). So far, have only used it in visual testing scenarios.
                                            >
                                            >
                                            >
                                            >
                                            >
                                            > To unsubscribe from this group, send an email to:
                                            > ccd-newastro-unsubscribe@egroups.com
                                            >
                                            >
                                            >
                                            >
                                            >
                                            >
                                            > To unsubscribe from this group, send an email to:
                                            > ccd-newastro-unsubscribe@egroups.com
                                            >
                                            >
                                            >
                                          • Ron Wodaski
                                            Oops -- looks like I ve already given it a try. However, the only thing I attempted was in image of Jupiter using the Extender Q:
                                            Message 21 of 28 , Dec 7, 2000
                                            • 0 Attachment
                                              Oops -- looks like I've already given it a try. <g> However, the only thing
                                              I attempted was in image of Jupiter using the Extender Q:

                                              http://www.wodaski.com/wodaski/images/ST_237/Jupiter_st237_fsq_eq.jpg

                                              Not bad, but that's all I have so far. Based on experience with various
                                              cameras and scopes and mounts, it's a good combination if you get a mount
                                              good enough to give you 2 minutes unguided exposures at f/5. Say a G-11 goto
                                              if they pan out... <g>


                                              Ron Wodaski
                                              The New Astronomy Book Site - http://www.newastro.com



                                              -----Original Message-----
                                              From: KSBTK@HOME [mailto:ksbtk@...]
                                              Sent: Thursday, December 07, 2000 4:35 PM
                                              To: ccd-newastro@egroups.com
                                              Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                              Ron - if I may be so bold - when you do image with the FSQ-106, could you
                                              please acquire some images with the ST-237. This is a combination that I
                                              may add to my wish list, pending your review.

                                              Clear skies,
                                              Kevin
                                              ksbtk@...

                                              ----- Original Message -----
                                              From: "Ron Wodaski" <ronw@...>
                                              To: <ccd-newastro@egroups.com>
                                              Sent: Thursday, December 07, 2000 6:27 PM
                                              Subject: RE: [ccd-newastro] Re: Flat fields with the ST-237


                                              > The goto version uses server motors, not the Hurst steppers that have been
                                              > problematic for some. I tested last night for visual only -- no real polar
                                              > alignment, just sighted Polaris through the borehole. I got really good
                                              > pointing accuracy, could have put objects on an ST-7E chip in the FSQ-106.
                                              >
                                              > I had the FSQ-106 on it, with the Megrez piggy-backed to add some weight
                                              to
                                              > really test it out. I will image with it on the next clear night. So far,
                                              my
                                              > experiences have been pretty positive.
                                              >
                                              > Ron Wodaski
                                              > The New Astronomy Book Site - http://www.newastro.com
                                              >
                                              >
                                              >
                                              > -----Original Message-----
                                              > From: KSBTK@HOME [mailto:ksbtk@...]
                                              > Sent: Thursday, December 07, 2000 3:00 PM
                                              > To: ccd-newastro@egroups.com
                                              > Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237
                                              >
                                              >
                                              > Thanks Ron - I sincerely appreciate it.
                                              >
                                              > I am extremely interested in your evaluation of the G-11 with goto. Do
                                              you
                                              > expect this to improve the tracking capability of the mount, particularly
                                              > with respect to CCD imaging? What scope are you using with the mount?
                                              The
                                              > FSQ-106 by chance?
                                              >
                                              > Clear skies,
                                              > Kevin
                                              > ksbtk@...
                                              >
                                              > From: "Ron Wodaski" <ronw@...>
                                              >
                                              > > I'm downloading your images now; will have critique later today.
                                              > >
                                              > > I've been unexpectedly occupied; I had a mount arrive for review/testing
                                              > > that is a prototype that a lot of folks will be interested in (G-11 with
                                              > > Gemini goto). So far, have only used it in visual testing scenarios.
                                              >
                                              >
                                              >
                                              >
                                              >
                                              > To unsubscribe from this group, send an email to:
                                              > ccd-newastro-unsubscribe@egroups.com
                                              >
                                              >
                                              >
                                              >
                                              >
                                              >
                                              > To unsubscribe from this group, send an email to:
                                              > ccd-newastro-unsubscribe@egroups.com
                                              >
                                              >
                                              >




                                              To unsubscribe from this group, send an email to:
                                              ccd-newastro-unsubscribe@egroups.com
                                            • KSBTK@HOME
                                              Good Morning Ron: Did you get an opportunity to evaluate the images? Sorry to pester you about this but I don t want to do any further imaging until I feel as
                                              Message 22 of 28 , Dec 8, 2000
                                              • 0 Attachment
                                                Good Morning Ron:

                                                Did you get an opportunity to evaluate the images? Sorry to pester you
                                                about this but I don't want to do any further imaging until I feel as though
                                                I am genereating useful flat fields. Looking forward to your comments.

                                                Clear skies,
                                                Kevin
                                                ksbtk@...

                                                From: "Ron Wodaski" <ronw@...>

                                                > There is a Fastar flat field sample on this page, about half way down:
                                                >
                                                > http://www.wodaski.com/wodaski/review_fastar.htm
                                                >
                                                > I recently took images of M34 and M38; both are relatively open. M34 is
                                                the
                                                > more sparse. But just about any random star field outside of the Milky Way
                                                > will do the job. if it is near the zenith and in the darkest portion of
                                                your
                                                > sky, even better; fewer light pollution issues to deal with.
                                              • Ron Wodaski
                                                Yes, I did. The flat fields look to be quite good; certainly, on the Horsehead image, I couldn t find any flaws. However. On the green image of the Horsehead,
                                                Message 23 of 28 , Dec 8, 2000
                                                • 0 Attachment
                                                  Yes, I did. The flat fields look to be quite good; certainly, on the
                                                  Horsehead image, I couldn't find any flaws.

                                                  However. On the green image of the Horsehead, your dark frame is very
                                                  ineffective, leaving many uncorrected hot pixels that show up as green dots
                                                  scattered all over the final image. I have no idea why this should be, but
                                                  it's a good example of why taking three of each type of image and median
                                                  combining helps.

                                                  FWIW, rather than apply the various flat fields to their corresponding color
                                                  light image, I averaged (median combined in maxim) all three together to get
                                                  a clean, less noisy flat frame, and this was very effective.

                                                  The red and blue images are nicely corrected by your dark frame, BTW; it's
                                                  just the green channel that is weird. I did notice that the actual
                                                  temperature for the camera was 0.5 degrees warmer for the green exposure;
                                                  that may have something to do with it.

                                                  This is not bad at all for a single set of 60-second exposures, but having
                                                  10-20 sets of RGB images would really take this to another level. <g> I
                                                  strongly urge you to get at least three of each calibration image. You have
                                                  hardly any dust bunnies on your optics, so I think you can safely use the
                                                  same flat field for your clear/R/G/B images.

                                                  I uploaded my color combine, with no Photoshop corrections, just histogram
                                                  scaling in Maxim, here:

                                                  http://www.egroups.com/files/ccd-newastro/Feedback/ST237+images%2C+dark+and+
                                                  flat+fi/HroseRGB.jpg

                                                  That's long enough that it will split onto two lines, so you'll need to
                                                  reconstruct the URL. <g>

                                                  Ron Wodaski
                                                  The New Astronomy Book Site - http://www.newastro.com



                                                  -----Original Message-----
                                                  From: KSBTK@HOME [mailto:ksbtk@...]
                                                  Sent: Friday, December 08, 2000 3:26 AM
                                                  To: ccd-newastro@egroups.com
                                                  Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                                  Good Morning Ron:

                                                  Did you get an opportunity to evaluate the images? Sorry to pester you
                                                  about this but I don't want to do any further imaging until I feel as though
                                                  I am genereating useful flat fields. Looking forward to your comments.

                                                  Clear skies,
                                                  Kevin
                                                  ksbtk@...

                                                  From: "Ron Wodaski" <ronw@...>

                                                  > There is a Fastar flat field sample on this page, about half way down:
                                                  >
                                                  > http://www.wodaski.com/wodaski/review_fastar.htm
                                                  >
                                                  > I recently took images of M34 and M38; both are relatively open. M34 is
                                                  the
                                                  > more sparse. But just about any random star field outside of the Milky Way
                                                  > will do the job. if it is near the zenith and in the darkest portion of
                                                  your
                                                  > sky, even better; fewer light pollution issues to deal with.





                                                  To unsubscribe from this group, send an email to:
                                                  ccd-newastro-unsubscribe@egroups.com
                                                • KSBTK@HOME
                                                  Good evening Ron: Thanks for examining the flat fields/images for me. Based upon your evaluation, I will continue to generate the flats as I di when in Fastar
                                                  Message 24 of 28 , Dec 8, 2000
                                                  • 0 Attachment
                                                    Good evening Ron:

                                                    Thanks for examining the flat fields/images for me. Based upon your
                                                    evaluation, I will continue to generate the flats as I di when in Fastar
                                                    mode.

                                                    I have a few questions about your observations, included in the text below.

                                                    ----- Original Message -----

                                                    > However. On the green image of the Horsehead, your dark frame is very
                                                    > ineffective, leaving many uncorrected hot pixels that show up as green
                                                    dots
                                                    > scattered all over the final image. I have no idea why this should be, but
                                                    > it's a good example of why taking three of each type of image and median
                                                    > combining helps.

                                                    Based on an earlier recommendation from you, I routinely take 5 dark frames
                                                    for each exposure length that I am using. I simply sent one so as not to
                                                    overburden you with the favor that I had asked.

                                                    Question - for "ultimate" calibration, how many dark frames and flat fileds
                                                    do you recommend?

                                                    > FWIW, rather than apply the various flat fields to their corresponding
                                                    color
                                                    > light image, I averaged (median combined in maxim) all three together to
                                                    get
                                                    > a clean, less noisy flat frame, and this was very effective.

                                                    Question - is this how you recommend the flat fileds be utilized or is it
                                                    better to use each for each color?

                                                    > The red and blue images are nicely corrected by your dark frame, BTW; it's
                                                    > just the green channel that is weird. I did notice that the actual
                                                    > temperature for the camera was 0.5 degrees warmer for the green exposure;
                                                    > that may have something to do with it.
                                                    >
                                                    > This is not bad at all for a single set of 60-second exposures, but having
                                                    > 10-20 sets of RGB images would really take this to another level. <g> I
                                                    > strongly urge you to get at least three of each calibration image. You
                                                    have
                                                    > hardly any dust bunnies on your optics, so I think you can safely use the
                                                    > same flat field for your clear/R/G/B images.

                                                    I actually collected 25 each of RGB. I need to collect additional clear
                                                    images.

                                                    Question - When I combine these, should I do them in groups of 5 (or some
                                                    similar number)?

                                                    Again, thanks Ron!!!!!

                                                    Clear skies,
                                                    Kevin
                                                    ksbtk@...
                                                  • Ron Wodaski
                                                    For the hubble, I believe that use something on the order of 50 or so frames before averaging. Feel free to use as many as you like. You need at least
                                                    Message 25 of 28 , Dec 8, 2000
                                                    • 0 Attachment
                                                      For the hubble, I believe that use something on the order of 50 or so frames
                                                      before averaging. Feel free to use as many as you like. <g> You need at
                                                      least three to do a median combine. 4, 5 etc. are better because they reduce
                                                      noise. But each additional image has less impact than the one before it, and
                                                      you rapidly get diminishing returns. The most I use is around 8, sometimes
                                                      12 for flats if there are some variations due to lighting conditions.
                                                      Generally speaking, I'm often pleased with 3, and will do up to 5 for
                                                      special occasions or important images.

                                                      It is optimal to take flats for each color. But I couldn't see any visible
                                                      difference in your case because the optics looked really clean. So it
                                                      depends; if you like the results you get with averaged colors, or just the
                                                      clear filter, you can use it. One would have to test to see the difference.
                                                      Another approach would be to carefully balance the average levels in the
                                                      flats, and then subtract one from another to see what's left. That
                                                      difference would tell the story.

                                                      When I am doing a color combine in maxim, I load all of the images into
                                                      Maxim at one time. In some cases, that is 30 or more images. I then
                                                      calibrate all of the images (or, more properly, as I learned today, do a
                                                      data reduction <g>), and then do an alignment using ever single image I've
                                                      collected at one time. I do 95% of my alignments manually because with most
                                                      packages, I can do a better job than the software can. I will do down to .1
                                                      pixel in up/down/left/right, and down to 0.01 pixel on rotations (for long
                                                      sequences, subtle rotation can occur from even the very slightest
                                                      misalignment to the pole). I then save every file adding " cal align" to the
                                                      end of the filename so I can retain my original data.

                                                      Then I combine each channel (LRGB), all of the files for that channel at one
                                                      time. I never do summing these days, just median combine, so I can do as
                                                      many at one time as I like. I get very smooth, low-noise images this way. I
                                                      posted comparison M33 images a while back in the alt.binaries.pictures.astro
                                                      newsgroup that showed how dramatically better median combining is to
                                                      individual images. I've done various summing/median combine comparisons, and
                                                      I can never see any substantive differences, and median combining is very
                                                      much easier to do, and is often better because it is very good at cleaning
                                                      out data extremes such as cosmic ray hits and satellite tracks.

                                                      This yields a single master image for each channel. I subtract a value that
                                                      gives me a 50-count average background using Pixel Math in Maxim, to get all
                                                      of the files so they have the same background level.

                                                      NOTE: If there are significant variations in background level, I will adjust
                                                      background levels of all of the individual images after I calibrate and
                                                      before I align. This greatly assists visualizing the exact degree of
                                                      misalignment; with equal background levels (this is called normalization),
                                                      the stars are also of equal brightness and it is easier to overlap them
                                                      exactly. When you do this, there usually isn't any need to do it again at
                                                      the late stage mentioned above. It appears that one gets better clarity and
                                                      smoothness in images that are normalized for average background value prior
                                                      to a median combine.

                                                      Ron Wodaski
                                                      The New Astronomy Book Site - http://www.newastro.com



                                                      -----Original Message-----
                                                      From: KSBTK@HOME [mailto:ksbtk@...]
                                                      Sent: Friday, December 08, 2000 3:02 PM
                                                      To: ccd-newastro@egroups.com
                                                      Subject: Re: [ccd-newastro] Re: Flat fields with the ST-237


                                                      Good evening Ron:

                                                      Thanks for examining the flat fields/images for me. Based upon your
                                                      evaluation, I will continue to generate the flats as I di when in Fastar
                                                      mode.

                                                      I have a few questions about your observations, included in the text below.

                                                      ----- Original Message -----

                                                      > However. On the green image of the Horsehead, your dark frame is very
                                                      > ineffective, leaving many uncorrected hot pixels that show up as green
                                                      dots
                                                      > scattered all over the final image. I have no idea why this should be, but
                                                      > it's a good example of why taking three of each type of image and median
                                                      > combining helps.

                                                      Based on an earlier recommendation from you, I routinely take 5 dark frames
                                                      for each exposure length that I am using. I simply sent one so as not to
                                                      overburden you with the favor that I had asked.

                                                      Question - for "ultimate" calibration, how many dark frames and flat fileds
                                                      do you recommend?

                                                      > FWIW, rather than apply the various flat fields to their corresponding
                                                      color
                                                      > light image, I averaged (median combined in maxim) all three together to
                                                      get
                                                      > a clean, less noisy flat frame, and this was very effective.

                                                      Question - is this how you recommend the flat fileds be utilized or is it
                                                      better to use each for each color?

                                                      > The red and blue images are nicely corrected by your dark frame, BTW; it's
                                                      > just the green channel that is weird. I did notice that the actual
                                                      > temperature for the camera was 0.5 degrees warmer for the green exposure;
                                                      > that may have something to do with it.
                                                      >
                                                      > This is not bad at all for a single set of 60-second exposures, but having
                                                      > 10-20 sets of RGB images would really take this to another level. <g> I
                                                      > strongly urge you to get at least three of each calibration image. You
                                                      have
                                                      > hardly any dust bunnies on your optics, so I think you can safely use the
                                                      > same flat field for your clear/R/G/B images.

                                                      I actually collected 25 each of RGB. I need to collect additional clear
                                                      images.

                                                      Question - When I combine these, should I do them in groups of 5 (or some
                                                      similar number)?

                                                      Again, thanks Ron!!!!!

                                                      Clear skies,
                                                      Kevin
                                                      ksbtk@...






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