Re: ATM 8" f3.8 -- Worthy project?

[astro.electronic@t-online.de (Michael Koch)]

Hi Matt,

> A couple of quick questions:  How  many folks have made sub f/4 smallish
>   mirrors? 

I made a 6" f/3.4 some years ago. That was my first selfmade mirror and I had no 
problems figuring it to about 1/5 wave. I used only the instructions from 
Texereau's "How to make a telescope".

> I'd like to see if I can figure his mirror, but, are there testing
> limitations or impossible coma problems at f/3.8?

I tested my mirror with a foucault tester exactly as described in Texereau's 
book. No problem.

Of course this mirror produces strong coma, but with the 20mm Nagler the image 
is acceptable.
Much better for this scope is the 20mm Brandon eyepiece with built-in coma 
corrector. As far as I know this eyepiece is no longer produced. Does anyone 
know if this eyepiece is still available somewhere? 

Michael

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 ASTRO ELECTRONIC  Dipl.-Ing. Michael Koch
         www.astro-electronic.de
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