"Martin R. Howell" writes:

On nights of exceptional seeing conditions, why not fully dark adapt your
eyes and see just how faint your scope can go? I have posted an image
which labels the stars in the immediate area of Messier 57 with their
magnitudes on my website.

Thanks for posting the labeled image. I know you intended this
exercise to be visual but, as a result of some recent experiments with
balancing my homebuild 10" Newtonian on a Vixen GP-DX mount for CCD
imaging, I had this 60 sec unguided exposure of M57 to compare
with. My results: anything above mag 17 is glaringly obvious, the 17.3
star is still easy, while the 17.7 one cannot for sure be
distinguished from the background noise.

pej
--
Per Erik Jorde