Re: Re:ATM Cassegrain as second telescope project.

[William Mc Hale <wmchal1@umbc.edu>]

On Tue, 6 Aug 2002, Bob May wrote:

>
> Actually Bill, the coma in a Cassegrain is dependent upon it's set of curves
> used with the proper Ritchey-Chretien design being 0 coma.  On the other
> hand, the one with the spherical primary (no corrector) will produce a lot
> more coma than an equivalent Newt.
> If you go past the RC design, you can even have inverse coma!
> The Cass designs do suffer from other problems although the general rule is
> that anything around the RC set of curves will produce a lot less error than
> a Newt. will.

Sorry I was a little sloppy with my terminology.  Where I said Cassegrain,
I meant classical Cassegrain, i.e. it uses a parababolic primary.

> I wonder what a Schmidt corrector version of the primary for the RC would do
> for performance?

Not sure if there is much to gain; well maybe you could design a corrector
that would correct for astigmatisim which I understand is still a problem
with the R-C design.

As it is for visual use, the field curvature is of greater importance than
Coma on most SCTs and Classical Cassegrains (or RCs).

Bill

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