Re: [APML] 'challenge'

[astropix@att.net]

 Hello John...

     Your diversity of film techniques... and the results you've attained... 
have served as inspiration to myself and many others, I'm sure. Your 
comparision of Regulus and Leo 1 is even more on point than the Jupiter/M44 
transit... both are outstanding images, IMO. I'm a little more encouraged for 
my chances with the equipment I have to use after seeing the Leo 1 shot, thanks 
for posting it!

Your comments concerning Catadioptics are also spot-on... perhaps a little 
understated... a large, well baffled APO is almost certain to win out on this 
one. The MN-71 I have has broadband anti-reflective coatings on the meniscus 
and the mirrors tested 97.3% reflectivity... with its 18% central obstruction 
and tube baffles (even the dew shield has a baffle!) I hope to have a close 
second. Colimation will be critical here... my laser colimator will center the 
secondary precisley, but with Intes practice of coring the primary combined 
with the secondary off-set... it takes sight tube and star tests to nail it 
down. I'll (hopefully) be tweaking this in days to come.

The apeture of this instrument is 180mm f/6... any ideas on the diameter for my 
diffraction cross? I need to keep this obstruction to a minimum... but how 
small is too small? Would .030" be a good starting point? .020"... ?

Thanks...

Geoff

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