As far as stellar limiting magnitude goes a pretty good formula to use is:
V = 15 + 5 * LOG10( D / 8 )
where D is the primary diameter in inches, and V will be your limiting
visual magnitude under a good dark sky.
Of course, individuals will have variations in their sensitivity, but this
is a pretty good average for a trained observer using averted vision and
detecting the object at about the 50% level. Part of the difficulty in
coming up with a precise formula, is determining what constitutes
"visibility". As the object becomes fainter near your limit, the
statistical behavior of the small number of incident photons will become
apparent. Rather than seeing the object steadily, like a bright star, you
will notice it tends to flicker in and out, as the individual photons
arrive randomly and less frequently. One measure of the "limit" is when
you can see the star about 50% of the time using averted vision, which is
the basis for the formula above.
Mike Linnolt
On Tue, 22 Mar 2005, Mark Wagner wrote:
>
> I know I've seen it out there before, but does anyone have a quick
> reference to the theoretical limiting magnitudes for various size amateur
> telescopes? I'd like to compare what I saw recently in my 10" f/5.7 with
> theory...
>
Received on Tue Mar 22 15:16:25 2005