Hi Lenny,

You could be right that light leakage may be the problem. You should be able to spot this easily in your master dark by stretching the image.
I usually perform my darks in a more controlled environment and build up a library of master darks for all the usual exposure times that I use. I am consistent with the temperature that I use (-10) and always use the same gain and offset etc. So this makes a library of master darks pretty convenient and allows more time to concentrate on getting enough lights flats and dark flats etc. Using a cooled camera also makes this really easy.
Good luck

Mike

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