Well I think I got some pretty good guiding with my Meade lx200 at 2500mm FL
I used an 80 mm f5 I believe. 400mm. Ratio 6:1. So the answer is....great mount? Can't say. I had about .3 pic then too. I didn't image though.
Not that I would recommend it but good pic with great PA and low periodic error and periodic error correction don't require much guiding over say a 2 minute exposures. So that is part of the answer. Our scopes however have a lot of PE and must be guided especially at high f#. We have seen some pretty nice iexos photos unguided for two minutes but at high field of view. Heck with low enough f#s you can get some nice pics In alt Az .
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired