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The donut is a dust mote in the imaging train (not the camera or nosepiece tough, it's much farther) that wasn't flat fielded. The lines in your second shot are a read out artefact. Usually happens in warm weather. Check your master bias to see if it has the same lines. Otherwise it might be in one of your subs in the stack.
Last edited by multiweb; 03-01-2011 at 11:29 PM.
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