Hello Eric,
Thanks for your further thoughts. Just playing the devil's advocate here, might my refractor be somewhat less sensitive to things such as non-orthogonal secondaries. etc when considering if a flat might help with the initial alignment of the rotator? I am of the opinion that I must do my very best to at least place the rotator as close to square as I possibly can. At this point the only "solutions" seem to be using a laser to aim at a mask over the objective, or "maybe" look at some flats to see if vignetting is even. Perhaps even a combination of both ideas would prove of some benefit. I don't know. (Josh suggested using a lathe with a dial indicator. Nice idea but I think impractical. How would I hold the OTA? And I don't have access to a lathe!).
I know that the earlier idea of putting a camera directly on the OTA is no longer under consideration, however, you did ask about numbers from my rotator test: The rotator was 20 feet (ca 6,000mm) from the wall and the beam moved a max of ~10 mm from center in a complete rotation. There are also 2 times where the displacement is quite rapid, almost like something is slipping in the rotator. I'd appreciate it if you could take a look at this video and give an opinion. Normal? Each square is 5x5mm.
https://drive.google.com/file/d/14PY...ew?usp=sharing
Thanks,
Peter