RE: [APML] Cassegrain notes

[Jon Kolb <jkolb@mindport.com>]

Roland, Tony,

I've got two questions:

1) 

> You are correct, when primary and secondary are the same, the field is
flat, but the 
> secondary obstruction is 50% or more for a typical film format. 

For purely photographic purposes, the literature I've seen (a small amount,
I'll admit), claims that the central obstruction is usually not the primary
concern compared to other aberrations.  What is the bigger issue here, the
central obstruction or the other aberrations, keeping in mind the "purely
photographic" nature of the problem?

2) Is the market demand for the "purely photographic" instrument too small
to justify producing scopes with an inherently flat field, despite the
necessarily larger size of the secondary obstruction?

Sincerely,
Jon Kolb
Adventures in Astrophotography
http://home.datawest.net/jkolb/
jkolb@mindport.com


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