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73930Re: [ccd-newastro] Do Dark and Bias Frame patterns change as the camera gets older over time?

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  • Ron Wodaski
    Feb 5, 2014
      it's not just those hot pixels; all of the pixels drift to some extent. Some are just more obvious.

      The only way to know how much, of course, is to compare sets against each other.

      Ron W

      On Feb 5, 2014, at 7:29 PM, Tim Stone <tim.stone.piano@...> wrote:


      I do believe the electronic characteristics of a CCD (can't speak for CMOS) changes over time. I notice new column artifacts, hot pixels, and such every now and then. When your calibrations are leaving these artifacts in the images, it's time for new calibrations. I'm with Mark... I tend to do new darks in December and June (cloudy nights, of course). Ambient temperature seems to affect them, and so I try to use darks that are no more than six months old, taken at the operating AND ambient temperature (average) I expect for the next few months. In other words, darks shot at -30C operating temperature with 20C ambient (50C delta) are less useful than darks shot at -30C and 0C ambient, if tonight's temperature is 0C. That's my humble opinion...

      Tim Stone

      On Wed, Feb 5, 2014 at 8:45 PM, Mark Acker <markacker@...> wrote:

      I think most take darks no more than about every 6 months or so.  Bias, since they take no time at all, can certainly be made anytime.  I will certainly defer to the experts in this forum, but that's about how ofter I redo them.
      Mark Acker

      From: cpatel823 <cpatel823@...>
      To: ccd-newastro@yahoogroups.com
      Sent: Wednesday, February 5, 2014 6:42 PM
      Subject: [ccd-newastro] Do Dark and Bias Frame patterns change as the camera gets older over time?

      Hi, I searched for an answer but cannot find a posting that speaks specfically to this. I took a library of Darks and Bias frames back in 2007. I try and adhere to specific temp and time parameters (15 minute exposures at -X degrees, while imaging to match images with reduction frames. My question is - Its been 7 years so do Dark and Bias frame patterns created by a camera change over time and should I recreate my library?

      Thanks for your input - Chris!

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