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Re: [ccd-newastro] Flats for each filter?

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  • arthurslevine
    Hi Mark Does this hold true for darks as well? I seem to remember that each filter should have its own darks. Thanks, Art ... From: Mark de Regt
    Message 1 of 8 , Apr 14, 2013
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      Hi Mark


      Does this hold true for darks as well?


      I seem to remember that each filter should have its own darks.


      Thanks,


      Art



      -----Original Message-----
      From: Mark de Regt <deregt@...>
      To: ccd-newastro <ccd-newastro@yahoogroups.com>
      Sent: Sun, Apr 14, 2013 1:21 pm
      Subject: RE: [ccd-newastro] Flats for each filter?





      Adding to that, keep in mind that flats correct not just for "normal" optical imperfections, but for dust donuts. In a pinch, you can substitute another filter's flats, but your results likely will be suboptimal.

      Mark

      -----Original Message-----
      From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On Behalf Of Mark Acker
      Sent: Sunday, April 14, 2013 10:51 AM
      To: ccd-newastro@yahoogroups.com
      Subject: Re: [ccd-newastro] Flats for each filter?

      Yes as each will have its own optical aberrations.

      Mark

      ________________________________
      From: Mark Striebeck <mark.striebeck@...>
      To: ccd-newastro@yahoogroups.com
      Sent: Sunday, April 14, 2013 12:22 PM
      Subject: [ccd-newastro] Flats for each filter?


      Hi,

      Do you create flats for each filter?

      MarkS

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      [Non-text portions of this message have been removed]

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    • Mike Dodd
      ... Art, No. Darks capture the _dark_ current of the camera chip. The shutter is closed, o it doesn t matter what (if any) filter is in front of the chip. Flat
      Message 2 of 8 , Apr 14, 2013
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        spaceage1939@... wrote:
        > Does this hold true for darks as well?
        >
        > I seem to remember that each filter should have its own darks.

        Art,

        No.

        Darks capture the _dark_ current of the camera chip. The shutter is
        closed, o it doesn't matter what (if any) filter is in front of the chip.

        Flat frames capture the _optical_ characteristics of the system,
        including vignetting, scratches, and dust motes on any glass surface
        between the objective end of the OTA and the camera chip. This includes
        the objective lens, mirrors, filters, and the cover glass over the
        camera chip.

        HTH.

        --
        Mike

        Mike Dodd
        http://astronomy.mdodd.com
        Louisa County, Virginia USA N37.58.23 W77.56.24
      • Audie Hickey
        Hi Art,   Exposures can need matching darks.  If the exposure is a flat then...maybe.  Really clear right...   Short flat exposures can use just a Bias
        Message 3 of 8 , Apr 14, 2013
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          Hi Art,
           
          Exposures can need matching darks.  If the exposure is a flat then...maybe.  Really clear right...
           
          Short flat exposures can use just a Bias exposure (very short dark).  However, if like me, you have a flat for red filter with an EL panel that takes 45 seconds, then a 45 second dark at the same temperature is handy to have.  The "maybe" in the second sentence.
           
          In general I use Bias frames, Darks and flats whenever I process an image.  I have separate flats for each filter and each angle of the rotator.  It works for me. 
           
          It is super easy to get darks on cloudy nights when you cannot image.  I usually just set things up in the garage and let it run with a sequence in Maxim.  I just have many darks at different times.  There are enough cloudy nights I have darks that I have never needed to use.
           
          There are things to scale darks, but I try to not use that approach if possible.  Hence the "can" in the first sentence. 
           
          Audie
           
           


          ________________________________
          From: "spaceage1939@..." <spaceage1939@...>
          To: ccd-newastro@yahoogroups.com
          Sent: Sunday, April 14, 2013 7:30 PM
          Subject: Re: [ccd-newastro] Flats for each filter?


           

          Hi Mark

          Does this hold true for darks as well?

          I seem to remember that each filter should have its own darks.

          Thanks,

          Art

          -----Original Message-----
          From: Mark de Regt <mailto:deregt%40earthlink.net>
          To: ccd-newastro <mailto:ccd-newastro%40yahoogroups.com>
          Sent: Sun, Apr 14, 2013 1:21 pm
          Subject: RE: [ccd-newastro] Flats for each filter?

          Adding to that, keep in mind that flats correct not just for "normal" optical imperfections, but for dust donuts. In a pinch, you can substitute another filter's flats, but your results likely will be suboptimal.

          Mark

          -----Original Message-----
          From: mailto:ccd-newastro%40yahoogroups.com [mailto:mailto:ccd-newastro%40yahoogroups.com] On Behalf Of Mark Acker
          Sent: Sunday, April 14, 2013 10:51 AM
          To: mailto:ccd-newastro%40yahoogroups.com
          Subject: Re: [ccd-newastro] Flats for each filter?

          Yes as each will have its own optical aberrations.

          Mark

          ________________________________
          From: Mark Striebeck <mailto:mark.striebeck%40gmail.com>
          To: mailto:ccd-newastro%40yahoogroups.com
          Sent: Sunday, April 14, 2013 12:22 PM
          Subject: [ccd-newastro] Flats for each filter?


          Hi,

          Do you create flats for each filter?

          MarkS

          [Non-text portions of this message have been removed]

          [Non-text portions of this message have been removed]

          ------------------------------------

          [Non-text portions of this message have been removed]




          [Non-text portions of this message have been removed]
        • arthurslevine
          Thanks Mike and Audie I appreciate the responses. Art ... From: Mike Dodd To: ccd-newastro Sent: Sun, Apr 14,
          Message 4 of 8 , Apr 15, 2013
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            Thanks Mike and Audie


            I appreciate the responses.


            Art



            -----Original Message-----
            From: Mike Dodd <mike@...>
            To: ccd-newastro <ccd-newastro@yahoogroups.com>
            Sent: Sun, Apr 14, 2013 9:54 pm
            Subject: [ccd-newastro] Re: Flats for each filter?





            spaceage1939@... wrote:
            > Does this hold true for darks as well?
            >
            > I seem to remember that each filter should have its own darks.

            Art,

            No.

            Darks capture the _dark_ current of the camera chip. The shutter is
            closed, o it doesn't matter what (if any) filter is in front of the chip.

            Flat frames capture the _optical_ characteristics of the system,
            including vignetting, scratches, and dust motes on any glass surface
            between the objective end of the OTA and the camera chip. This includes
            the objective lens, mirrors, filters, and the cover glass over the
            camera chip.

            HTH.

            --
            Mike

            Mike Dodd
            http://astronomy.mdodd.com
            Louisa County, Virginia USA N37.58.23 W77.56.24








            [Non-text portions of this message have been removed]
          • Mark de Regt
            As Mike said, no, you only need darks for each exposure time and temperature (I combine 25 darks to minimize noise), since darks are taken with the shutter
            Message 5 of 8 , Apr 15, 2013
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              As Mike said, no, you only need darks for each exposure time and temperature (I combine 25 darks to minimize noise), since darks are taken with the shutter closed. You may be thinking of the fact that darks, unlike flats, must be taken at the same binning as the light frame you're calibrating (i.e., if you're calibrating a 2x2 binned light frame, you have to use a dark frame--or frames--taken at that same binning; you can successfully resize a flat frame taken unbinned).

              Hope this helps.

              Mark

              -----Original Message-----
              From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On Behalf Of spaceage1939@...
              Sent: Sunday, April 14, 2013 7:31 PM
              To: ccd-newastro@yahoogroups.com
              Subject: Re: [ccd-newastro] Flats for each filter?

              Hi Mark


              Does this hold true for darks as well?


              I seem to remember that each filter should have its own darks.


              Thanks,


              Art



              -----Original Message-----
              From: Mark de Regt <deregt@...>
              To: ccd-newastro <ccd-newastro@yahoogroups.com>
              Sent: Sun, Apr 14, 2013 1:21 pm
              Subject: RE: [ccd-newastro] Flats for each filter?





              Adding to that, keep in mind that flats correct not just for "normal" optical imperfections, but for dust donuts. In a pinch, you can substitute another filter's flats, but your results likely will be suboptimal.

              Mark

              -----Original Message-----
              From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On Behalf Of Mark Acker
              Sent: Sunday, April 14, 2013 10:51 AM
              To: ccd-newastro@yahoogroups.com
              Subject: Re: [ccd-newastro] Flats for each filter?

              Yes as each will have its own optical aberrations.

              Mark

              ________________________________
              From: Mark Striebeck <mark.striebeck@...>
              To: ccd-newastro@yahoogroups.com
              Sent: Sunday, April 14, 2013 12:22 PM
              Subject: [ccd-newastro] Flats for each filter?


              Hi,

              Do you create flats for each filter?

              MarkS

              [Non-text portions of this message have been removed]

              [Non-text portions of this message have been removed]

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              [Non-text portions of this message have been removed]



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