Re: [ATM] Mersenne (was : Looking for information ona telescopedesign)

[David Weinshenker <daze39@earthlink.net>]

Jan Bentz wrote:
> 
> Doesn't it make much more sense to forget about the Mersenne
> configuration and use a standard Cassegrain format in a Naysmyth layout
> and bring out the focus through the altitude trunnion.  Fewer optical
> surfaces is always better for image quality and alignment.  The only
> real reason to use the Mersenne is if you must have a relatively fast
> system with less obstruction.

What looks good to me about the Nasmyth layout is that the final diagonal
mirror can be very small - meaning that it can be made a bit oversize
(relative to the net optical requirement), avoiding the edges of the glass
(which may be less perfectly flat than the center) and still be completely 
behind the shadow of the convex secondary, adding no extra obstruction!

-dave w
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