Many thanks for your reply, Pete. I'll re-ask the question in the astro forum.On the terminology, I think I meant a "dark" as opposed to a "dark flat", which is indeed as you describe.FYI, I've put two images here, one a dark taken as a RAW/NEF (whihc looks terrible) and one taken as a jpg, which looks the way I think it should look:downloads.archsoc.com User name: FriendsPassword friendsClick the links to download.Thanks for your time,Garry
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