I have recently purchased an RC 14" (Omegon; same model as the GSOs, TPOs, etc around). Coming from a Newton 12", the learning curve for collimation is brutal. I have tried to follow the DSI method, which is easy to understand and apply, but I'm hitting a problem that I can't trace. I'm hoping that someone will know what that is.
I can defocus a star and align primary, then move to a star field and align secondary as the method describes. I can have pretty good results:
The problem is that there is a clear distortion in the field that makes all that work useless because it's not on good bases. Here is a sequence going from outside focus to focus to inside focus. See how the stars are distorted one way before focus, then another after ocus.
Before I attempted DSI, I did a laser collimation (mostly following a method I used to apply to my Newtons):
First I adjust the focuser onto the secondary by using a laser (collimated best I could on a wall 6m away) and rotating it to make sure its dot in the secondary wobbled a bit, that's inevitable when you rotate by hand, but never enough to leave the center of the secondary (what is marked as center, obviously), or enough to describe a circle, by adjusting the focuser screws. I considered that this told be the focuser was in line with the optical line, assuming the secondary is centered. Then I center the reflection of the concentric rings onto the primary from the secondary (takes time; possibly readjust the focuser centering if you made big changes and start again a few times) by adjusting the secondary's screws. Then I center the concentric rings reflected onto the wall by the primary so that the secondary reflection (very faint light only visible in the dark) is centered with the rings from the laser and the rings are concentric and equally spaced.
I have done the whole thing every night from scratch (laser collimation to star test) for the last 4 nights and I'm not getting closer because I can't figure out what causes the star distortions.
Does anyone have an idea?
Edited by Cedric_r, 10 March 2021 - 03:26 AM.