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

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  • 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 1 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 2 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







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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 3 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 4 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 5 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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