Please don't shoot me if I am wrong, but from memory, coma in a classic cassegrain is the same as a newtonian of the same focal length. That is, the GSO f/12s would show the same coma as a f/12 newt.
That is certainly what the laws of optics tell us. There’s though more astigmatism and field curvature in CC compared to equal f-ratio & focal length Newt, both of which may also affect edge-of-field performance in CC.
If one doesn’t want to take my word on it, check e.g. telescope-optics.net for all the formulas, graphs and ray traces. ”Telescopes, Eyepieces & Astrographs” by Smith, Ceragioli and Berry (Willman-Bell) also has a nice treatise on the subject.
For subjective, personal experience, I invite people who have actually compared equal size, equal f-ratio CC and Newton to chime in. I certainly haven’t (although would love to! ;-)
Edited by Axunator, 13 November 2019 - 04:30 AM.