Re: [ATM] Posible variation on the Cassegrain secondary

[Jim Burrows <burrjaw@earthlink.net>]

At 2006-09-13 14:10 -0400, vladimir sacek wrote:

>Relatively small deviations in the secondary conic or ROC can be
>compensated by a slight change in mirror separation, keeping both
>spherical aberration and coma practically cancelled. It would be
>much harder to go for the exact match with the separation fixed.

Unfortunately, the OTA is already made and I think the back focus can't be 
much more than 300 mm, so I'm pretty much in the "much harder" 
situation.  The results of the last test say with that restriction the 
system wavefront RMS is HUGE (3620 nm); without the restriction, 429 nm 
with back focus 413 mm.  Maybe I should think about reducing the 429 nm (as 
you say, much easier) and fiddling with the OTA rather than continuing ad 
infinitum trying to reduce the RMS with restriction (best I've gotten is ~ 
500 nm, 12 spells ago <sob>).

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)  

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