Folks,
I’ve been experimenting with an f/4 newt for imaging, as a bit of a project. Given the lockdown I’ve finally had a little time to play with it.
Having collimated the scope in situ with Cats Eye autocollimator (secondary) and Barlowed laser (primary) in an iterative manner, if I turn the scope to a bright-ish star for star testing I find that the shadow of the secondary shifts position between roughly equivalent amounts of defocus intra and extra.
So far I’ve failed to get completely round stars when in focus...I always find something wrong with them. Night before last I got really close, where the smaller stars looked round but the larger ones appeared fat-bottomed. Not that there’s anything wrong with that, I just prefer my stars round
Can anyone shed any light on what might be happening?
Cheers,
Dunk