This is way too conservative. It yields about 15 for my 18". I've
actually seen into the low 16s with it.
By the way, formulas like this are empirical, not theoretical. In
order to be realistic, a formula needs to take magnification into
account. Also, most published magnitudes are for blue light, which
the eye is somewhat less sensitive to than green or white light.
Also, visibility of point-like stars can be far different than
visibility of extended and nebulous objects of the same magnitude.
The actual simple formula I've seen used most often is this:
M = K + 5 * log(D)
Where K is a constant which has a value of around 9.5 when D is
measured in inches.
D is the diameter of the aperture. But this formula is still wrong
for larger aperture.
Joe Huber wrote:
> Here is a link to Ken's Telescope Calculator - limiting magnitude is one of
> the calculations.
>
> http://www.klhess.com/telecalc.htm
Received on Tue Mar 22 14:55:59 2005