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Old 13-10-2019, 09:34 AM
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Atmos (Colin)
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Join Date: Aug 2011
Location: Melbourne
Posts: 6,980
What exposure were you using for the flats?
Did you use darks for the flats or a bias?

I’ve found that the best way to do flats with a CMOS is to NEVER use bias but have darks for the lights and darks for the flats. It does mean you want to have the same exposure for both darks and flats as best as possible though.

Over correction on flats in my experience is usually from poor flat calibration or trying to correct for too much vignetting. If the vignetting is too strong it appears as overly bright corners, at times not because it’s actually too bright but because of the lack of data and the artificial brightening.

I noticed this when using a DSLR on the RH200, the mirror box within the Nikon caused heavy vignetting that made the outer portions of the frame uncorrectable via flats.
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