Howdy folks. I'm a noob and have caught the astrophotography bug recently. I have a Celestron Evo 8 and have been having some trouble with sharpening focus on all objects; terrestrial, stars, moon, clusters, planets, etc. Some of the problem is clearly thermal and seeing issues with turbulence, but it can't explain why every single object is slightly out of focus. At first, I suspected fat fingers on the manual focuser so I bought the Celestron focus motor for super precise and no-hands focus. Didn't help.
Next, I suspected collimation problems, so last night I locked in on a mag 2 or 3 star near zenith (forgot which star exactly). I noticed that when I de-focused "in", I got a weird oblong or egg-ish shape on the "upper left" of the of the diffraction pattern, when I de-focused "out", the pattern looks spot on circular. My understanding is that the diffraction pattern should be the same shape independent of which way I de-focus (see figure 9 in the celestron collimation guide).
My rig was temperature stable as far as I know, and this problem reproduced using a 10mm eye piece as well as with my ZWO ASI224mc cam over the course of an hour. I attached are a couple shots and here is an avi showing the problem. Any ideas why I am seeing different shapes of diffraction based on focus direction? I don't want to mess with the collimation screws if this isn't due to mirror alignment.
Thanks in advance for any ideas, insight, wisdom!