I am struggling with trying to identify the cause of coma like aberration on an old C80 ED refractor. aside from the aberration, the focus is not bad across the field. I posted in the astrophotography forum and got a few answers suggesting tilt was the issue. I was told that in true coma, the tail points away from the centre which is opposite to what is seen here. So I purchased a tilt adjuster, but when I try and correct the coma that is occurring in one corner of the image, as expected the opposite corner gets further out of focus so the end result is worse than the original. I am a complete non expert on optics, but it looks to me when I look at my images from this scope, that the bottom left (as in this example) is the best and If I could move the image so that section was closer to the middle, I could improve the overall image.
this sope is relatively non adjustable. the focus rack and pion type is fixed, but I am wondering if there is a bench test I can use to further diagnose the problem and if for example rotating the objective elements might improve things. I could just give up on this scope, but I am hoping I could learn something about scope optics adjustments if this can be improved