I've noted of late my flats highlight some significant vignetting, quite asymmetrical on the chip - images certainly clean up with flat calibration, but with a small chip like mine, I think vignetting really shows I must be off in collimation somewhere.... I've checked with a glatter laser, seems ok... CCD inspector shows around 5-10" of miscollimation.... I've never actually tried the CCDi collimation utility (seems a waste of a clear night!
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This is with the f/4 newt, Atik 420, and Baader MPCC....
Any advice in getting to the bottom of this? With an increasing moon, might be a good time soon to dismantle and check everything....
Attached is a highly stretched flat, and a CCDi flat analysis....