Trying to determine if CCD is linear by observing pairs of stars at various exposure times. Finding that focus is bad !?Is it even possible to get ‘doughnut’ images for out-of-focus stars in a refractor?RH is 50%, T is about 44 F, wind is 6-8 mph- It seems clear.Later, osberving Moon: ..54.06.. T=37ish F, RH is down to 42%, wind 2-3 mph. seemed clear when the Moon rose.