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Re: [ccd-newastro] Flats

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  • Ron Wodaski
    1. Average value, brightest area of frame. That is an anti-bloomng chip, so it goes non-linear as it gets brighter. So your concern is that you stay below the
    Message 1 of 36 , Jul 16, 2010
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      1. Average value, brightest area of frame. That is an anti-bloomng chip, so it goes non-linear as it gets brighter. So your concern is that you stay below the non-linear zone everywhere. So measure against the brightest regioin. (Not brightest pixel; read an average value)

      2. Not the best approach. For flats, you will have to normalize the exposure times to avoid large errors. That will increase the noise contribution of the shorter exposures as they are normlaized.

      I would recommend you use one of the automation devices. You have only a small window of time to take flats, and you don't want to spend it trying to adjust your exposure times on the fly. Automation sofware will handle that for you.

      Ron Wodaski

      On Jul 16, 2010, at 3:18 PM, Jim wrote:

      > 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
      >
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      > ------------------------------------
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    • Roy Uyematsu
      I m sorry it is an Automatic Flats but it is preemptive. Roy Uyematsu www.roystarman.com roystarman@cfl.rr.com From: ccd-newastro@yahoogroups.com
      Message 36 of 36 , Jul 24, 2010
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        I'm sorry it is an Automatic Flats but it is preemptive.



        Roy Uyematsu

        www.roystarman.com

        roystarman@...



        From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On Behalf Of Roy Uyematsu
        Sent: Saturday, July 24, 2010 9:00 AM
        To: ccd-newastro@yahoogroups.com
        Subject: RE: [ccd-newastro] Re: Flats





        In CCDCommander the Flats command is called Wait Until Flats. It is preemptive, as it will go when the time is right and if you are imaging it will abandon the last one. Once there it takes Flats much quicker than a human since it is predicting the exposure time based on the previous exposures. You also set up the number of flats it you want filter and binning and let it run. Given the time for flats is normally past true Astronomical dark (about 1/2 hour before sunrise) it is unlikely you would be imaging in that time period. However you can also decide to do this at Dusk with the automation routines. I also believe you can program the degrees the sun is below horizon to get some more time. For these flat programs to work you need to make sure Lat/ Lon, Altitude and Time in your system is pretty accurate.

        Roy Uyematsu

        www.roystarman.com

        roystarman@... <mailto:roystarman%40cfl.rr.com>

        From: ccd-newastro@yahoogroups.com <mailto:ccd-newastro%40yahoogroups.com> [mailto:ccd-newastro@yahoogroups.com <mailto:ccd-newastro%40yahoogroups.com> ] On Behalf Of jfmiller7@... <mailto:jfmiller7%40comcast.net>
        Sent: Monday, July 19, 2010 6:34 PM
        To: ccd-newastro@yahoogroups.com <mailto:ccd-newastro%40yahoogroups.com>
        Subject: Re: [ccd-newastro] Re: Flats

        That sounds fantastic .

        thanks ,

        Jim
        ----- Original Message -----
        From: "Don Goldman" < donclearview @...>
        To: ccd-newastro@ yahoogroups .com
        Sent: Monday, July 19, 2010 11:01:43 AM
        Subject: [ccd-newastro] Re: Flats

        I've been using CCDAutoPilot for years to do dawn sky flats. I trained with Ron when I started imaging, and in those days, we didn't have these automated programs. Trying to take sky flats with the quickly change light conditions was impossible for me. These automation programs totally changed that. In CCDAp , you program in your flats (e.g. 5 red, 5 green.....). After you're done automatically taking your lights ( darks , biases), the scope is parked. When the sun is 8 deg below the horizon the scope is slewed to the "null point" in the sky near the zenith and waits. Then it starts taking quick exposures just in the center of the frame and adjusts the exposure to get a pre-programmed signal ( ADU ). I set mine to 30,000 ADU . It keeps adjusting the exposure so that all flats will roughly have this value, which makes making a master flat for each filter very easy. This also includes narrowbands , which need alot more light. Easy, because the sky is getting lighter with time. Once, done, CCDAp parks the scope, turns off the camera and the flats data are there when I wake up. Also, there is a FLATS NOW button such that if you are up at dawn or want to do this at dusk, it starts the procedure when you click the button. It really makes this stressful, but necessary task a no-brainer.

        Don Goldman
        Astrodon Imaging

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