Re: ATM Cassegrain as 2nd project / optics calculations

[Kevin McEnhill <mcenhillk@mac.com>]

Is there a way to deal with the field curvature? I have been thinking of 
an RC for a large deep sky camera but keep coming to this field 
curvature thing.

On an almost related note, where can I find information about optical 
design from a telescope point of view? I would like to be able to 
evaluate different designs but all I can find are subjective 
descriptions like the current thread. Software would be nice, but 
without access to a Windoze machine, I am at a loss. I have been 
considering the Advanced Telescope Making Techniques by Allan Mackintosh 
but have some reservations about buying another  $25.00 shelf queen. Any 
ideas.

Thanks.
Kevin McEnhill
mcenhillk@mac.com
You can have my Mac when you pry my cold dead fingers off of it.

On Tuesday, August 6, 2002, at 04:41 , William Mc Hale wrote:

>
> 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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