I've been using a StellaLyra 8"RC for a few months now, and with my Canon 60D it worked perfectly. Now I've got an ASI533-MC Pro, things are much more complex! I'm struggling to get stars in focus or round enough for DeepSkyStacker to stack the images properly, and other than the possibility of dew on the camera, I can't see why this might be.
Using a Bahtinov mask I'm getting perfect focus on bright stars, but the smaller stars in images of M51 recently seemed a bit naff. I therefore wanted to make sure I had my backfocus right!
According to the GSO online manual, the backfocus sho