How faint can your scope go?

In Rat's post of 9/7/04, he remarked on his observation of the Ring Nebula:

snip
M57 (of course) - Ring Nebula - PN - LYR - Wow, This is too fun! I noticed
a couple of faint stars, coming in and out of view, lying just outside the
ring (in addition to the Mag 13 one that I usually see), I am going to
check later and see what Mag they were.
unsnip

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. My 12.5 inch dob has revealed the 14.7 magnitude
star and using averted vision I can sometimes convince myself that the
neighboring 15.3 magnitude star is hinting at its presence.

To see the image, go to http://home.earthlink.net/~martinhowell and click
on "Other stuff"


Martin