quick note on Arne's picture of M31

[Stupendous Man <richmond@a188-l009.rit.edu>]

  I was just playing around with Arne's picture of M31, which is
a composite with total exposure time 103 minutes.  It shows stars
which are very roughly as faint as those which show up in a picture
of M31 I took with a Meade LX200 a few weeks ago here at RIT, which
had exposure time 90 seconds = 1.5 minutes.   The faintest stars I
can see clearly in each are around V = 17.

  If you want to compare them yourself, check out:

  Arne's Mark IV picture:  
         http://a188-l009.rit.edu/tass/markiv/flagstaff/m31.html

  Michael's LX200 picture:
         http://a188-l009.rit.edu/richmond/ritobs/oct12_2000/oct12_2000.html

  Let's see -- does this make sense?  

       Mark IV: aperture diameter =  10 cm
       LX200:                       100 cm
  
So, the LX200 has 100 times as much light gathering power as the Mark IV;
it's no wonder that the Mark IV takes a bit more time to detect stars
of the same brightness.  

  Okay, okay, it's not a completely fair contest: the Mark IV picture 
was taken through a V-band filter, and the LX200 picture through no filter;
the Mark IV had a much darker sky background; the LX200 is focused a bit
better.  But you get the general idea.

                                          Michael Richmond