Re: [ATM] Posible variation on the Cassegrain secondary

["John Moore" <jamooretx@web.com>]

Hi Jim,,

Hope this works-out for you,,
sorry your "cassegrain" is giving you fits,,
we feel your pain!,
hope the solution shows itself!,
were behind-you!!, and rooting for you!!,
wish I could help!, but I havent done a cassegrain, YET!
again,,hope things work-out!!!

John.
[PS; sorry mel, if I didnt reply correctly, Im still trying to 
figure-out how to get my responses at the end-of-the-thread?]
-----------------------------------------------

From: Jim Burrows <burrjaw@earthlink.net>
To: atm@atmlist.net
Subject: Re: [ATM] Posible variation on the Cassegrain secondary
Date: Wed, 13 Sep 2006 16:00:07 -0700


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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