I as just looking at coma correctors if I wanted to try an f5 instead of f6, and may have found a solution to both several problems at once.
Bintel Coma Corrector
https://www.bintel.com.au/product/bi...v=6cc98ba2045f
GSO Coma Corrector
https://agenaastro.com/gso-2-coma-corrector.html
This coma corrector has a back focus requirement of 75 - 80mm. So shouldn’t this mean no matter whether you throw it on an AP classed, or visual classed scope, it’ll provide plenty of back focus distance? At least for Canon Camera’s, with a standard back plane at 55mm, there should be room to spare. From what I’ve found so far, without any extra attachments, it’ll need a 15 or 20mm spacer to reach back focus.
So what am I missing here? If a coma corrector is recommended anyway (maybe not for an f6, but it can’t hurt) what’s bad about doing this, and why wouldn’t it be a universal solution to the question of whether there’s enough back focus or not on a particular scope?
The two main concerns I can think of is possible vignetting down the long focus path (easily corrected in post editing) and the extra long tube length throwing off mount balance and being slightly less stable mechanically and possible visually.
There must be a big gotcha - what am I missing?