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68358Re: New to CCD Astrophotography: Master Dark/Master Bias?

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  • evwark
    Nov 2, 2010
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      It would! But that's the problem. You don't want to take a new dark frame with every picture you take, so it's better to just take a master dark that you use again and again. But since light exposures aren't always all the same duration, you need to scale the dark frame (10m dark, 5m light? Just divide the dark pixel values in half!). But bias data doesn't scale, and if you leave it in, you can't scale the dark. Hence the subtraction.

      Of course, as I've learned, Maxim DL does all of that automatically. I'm just blown away by this software. It really does absolutely everything...

      --- In ccd-newastro@yahoogroups.com, jfmiller7@... wrote:
      >
      >
      >
      > Would not a dark frame already have bias data in it?
      >
      >
      >
      > regards ,
      >
      >
      >
      > Jim
      > ----- Original Message -----
      > From: "Douglas B. George" < dg @...>
      > To: ccd-newastro@ yahoogroups .com
      > Sent: Monday, October 25, 2010 2:26:47 PM
      > Subject: Re: [ccd-newastro] New to CCD Astrophotography : Master Dark/Master Bias?
      >
      >  
      >
      >
      >
      >
      > On 2010-10-25 11:43 AM, Neil Fleming wrote:
      >
      > > * The sources I've read suggest subtracting the bias frame from each dark
      > > sub-frame before combining them. But couldn't I combine, then subtract just
      > > once? Or is there a quirk of the algorithm that makes that a bad idea?
      >
      > That's a REALLY bad idea. Not because of any quirk, but because MaxIm DL
      > handles that automatically. Doing it manually will probably result in it being
      > done TWICE, which would be bad.
      >
      > The Set Calibration command is designed to handle everything automatically.
      > Just dump in all of your calibration frames and let it figure out the details.
      >
      > Doug
      >
      > --
      >
      > Doug George
      > dgeorge @...
      >
      > Diffraction Limited
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      > [Non-text portions of this message have been removed]
      >
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