Removed the CCD camera and filter wheel from the imaging scope, brought it indoors, and let it warm up. Then I checked the filters for cleanliness – they seem OK and I decided not to muck with them other than blowing dust off. Disassembled the CCD camera and found the protective window to be quite dirty with microscopic dust spots, so I cleaned this with 99% isoprop alcohol, both sides. The CCD itself seems ok, and I didn’t clean it except for gently blowing off dust.