Re: Is this tilt in the image train?
While most likely there are optical aberrations contribute to what you are seeing, there is a simple test that you can run to see how much tilt is affecting your image. Run a set of exposures from outside of focus to inside of focus. With the Nitecrawler on this OTA and camera, I would recommend starting about 1,000 steps outside of focus and moving in 250 steps at a time. If there is tilt in your system, there has to be a line with stars in focus that moves through your images with each frame. This will allow you to look at the shape of stars inside and outside of focus both on and off axis. If there are aberrations (coma, astigmatism, and curvature are prime culprits) due to misalignment of the four lenses, it will be very obvious.
I just went through this with the same OTA and camera this past Spring. I had been using my OTA with smaller sensors (ASI1600, Atik 383L+) and then a bigger sensor but with large pixels (FLI ML16200), which gave good results without any obvious star shape problems. When I put the ASI6200MM on the OTA in the Winter it was a mess. Using the Sidewinder I was able to get it to be somewhat acceptable but definitely not great. I sent the OTA to Houston in May and received it back in late August. It’s very much improved and after some minor adjustment for sensor tilt is now giving a tight star field all over the field of view.
From: firstname.lastname@example.org <email@example.com> On Behalf Of Tom Blahovici via groups.io
Sent: Monday, September 27, 2021 3:58 PM
Subject: Re: [ap-gto] Is this tilt in the image train?
The camera is a full frame ASI6200.