Re: [ATM] Cassegrain vs. Gregorian

[Michael Peck <mpeck1@ix.netcom.com>]

At 23:01 24-08-04, Richard F.L.R. Snashall wrote:
>  Given the same requirements (400 mm f/16, net length 1800 mm, body 
> length 1500 mm,
>0.36 degree (c. 40 mm) field diameters):
>



>Assuming a good method of testing the Cassegrain secondary, does this imply
>that the Cassegrain wins hands-down over the corresponding Gregorian, or
>is my comparison mixing apples and oranges?

Fixing the total length of the telescope is kind of an unusual design 
constraint, but why not? It makes for an interesting comparison at least. 
The Cassegrain is a very conservative, mainstream design. I'd guess that 
the Gregory secondary would be tough. For that matter the primary is under 
f/3, which makes it a challenge too.

Your conic constants are slightly off of the aplanatic solution. I get 
(-1.083, -4.839) for the Cassegrain primary and secondary; and (-0.985, 
-0.508) for the Gregory. The difference is a few thousandth's of a wave at 
the edge of the field.

Mike Peck


_________________

Michael Peck
email mpeck1@ix.netcom.com
Wildlife photography page http://home.netcom.com/~mpeck1/index.html
Amateur telescope making http://home.netcom.com/~mpeck1/astro/astro.html 

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