Quote:
Originally Posted by tonybarry
Hi Ray,
May I ask how you would know you had no vignetting or dust bunnies without taking at least one flat ?
Regards,
Tony Barry
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Easy, take a long exposure image where the sky glow is significantly above the read noise, e.g. any properly exposed sub. The bgd pedestal will show vignetting, dust bunnies, and with enough bgd signal (more than just above rad noise) ccd non-uniformity.
In Maxim there is a graph tool to plot the intensity as a function of position for a line you draw on the image, it can be quite disturbing when used on an SCT + focal reducer how vignetting actually happens...it convinced me my C14 had a limited life span
EB