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Flats

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  • Jim
    I have a question regarding flats. I have read up quite a bit on the subject, but I have two questions surrounding the process. First, the ADU recommended for
    Message 1 of 41 , Jul 16, 2010
      I have a question regarding flats. I have read up quite a bit on the subject, but I have two questions surrounding the process.

      First, the ADU recommended for my STL-11000 is I believe 25000. Would this be the center of the flat, or halfway between the centre or the edge?

      Second, I am taking sky flats, and with the sky changing at dusk and the god-awful download times of the STL at 1x1, the ADU of the flat frame can change between flats. Can I take a number of flats at different ADU counts, say 35000 to 20000 and then use a median or mean combine to use a useable master flat frame?

      Many thanks,

      Jim
    • Don
      Depending on the filter you are exposing through and brightness of the illuminated flat screen, your exposure time seems too long. You should expose for an
      Message 41 of 41 , Dec 9 11:23 AM

        Depending on the filter you are exposing through and brightness of the illuminated flat screen, your exposure time seems too long.  You should expose for an ADU count of approximately 25,000 to 30,000.  Start with short test exposures and work up until you get the ADU you want for the flat.  Use that time for your final flat exposure.

        Hope this helps,

        Don Waid

        http://www.waid-observatory.com

         

         

        From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]
        Sent: Saturday, December 09, 2017 11:09 AM
        To: ccd-newastro@yahoogroups.com
        Subject: [ccd-newastro] Flats

         



        This seems like a silly question, but if I am taking a flat (in my office) and walk around the room, could this cause weird looking image read outs?

        I am using Gerd Neumann's illuminated flat screen and shooting though a refractor with the QSI 683wsg with 5.9mm square pixels.

        When the image returns after a 300sec integration set at -20c, there are quite a few bold black lines on the left running vertically with a kind of chaotic pattern and mostly pure white everywhere else.

        Everything is mounted on a high end EQ mount, without any flexure.

        Hence my question.
        Thanks.
        Gregory Gig Harbor, WA.

         




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