From: "Mel Bartels" 
To: 
Reply-To: "Mel Bartels" 


>>>
    So why am I bothering with an observing report on a telescope making
forum?  If you're making a mirror and you're thinking of quitting at 1/4
wave because it's "diffraction limited", you may reach
"Dawes limit", but that's about all.  If you ever want to use
more 150 power on a planet, don't stop at 1/4 wave, don't stop at 1/8 wave.
 If you have to settle for 1/16 wave, you probably won't be too unhappy. 
So take the time, whatever it takes, to make it absolutely the best you
can, because eventually, you'll be glad you did.  It DOES make a
difference.
<<<

Actually, optical quality matters little in the detection of Cassini's
Division in a 60mm scope.  Much more important is control of scattered
light and appropriate magnification.  Same for deep sky fuzzies.

>>>
    How else could it be possible to detect a dark line .01" wide at 440x
with an 8" telescope?  Or a .7" power line naked eye?  And even
though it may not have appeared quite that small (maybe a few times that
wide) it sure didn't blur to the .5" Airy disc width.
<<<

My suggestion is to forget about the Airy disc for now.  It's confusing the
issue.  Resolution of lines on a contrasty background has little to do with
the Airy disc.  It has everything to do with the eye and the presentation
of the line/background to the eye.  Same thing for deep sky fuzzies.  The
Airy disc has nothing to do with resolving detail in M42 for instance.

Mel Bartels

--- BBBS/NT v4.00 MP