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The proof is in using the flat and does it correct the vignetting and any dust donuts?
I find around 18,000 ADU works for flats with various scopes and cameras.
Matched with accurate darks at the same temperature and perhaps a good bias (I don't always use a bias and always test before I calibrate a set of exposures).
I might also add the minimum exposure I go for is about 3 seconds but that is with cameras with a physical shutter. Less than that and you see artifacts from the shadow of the shutter. But for cameras with an electronic shutter like ZWO and QHY cameras this is not an issue.
Greg.
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