Re: [ATM] Aplanatic Gregorian (was: 25" mirror possibilities)

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Michael Lindner wrote:

>On Wednesday 24 November 2004 11:08 pm, lou krajci wrote:
>
>>...whip up aplanatic Gregorians.  If
>>nothing else...maybe we can come up with some simplifications/rules of
>>thumb...some starting points and examples for ATM's to start from.
>>
>
>Reading Schroeder's "Astronomical Optics" (which is indeed a $100 book!) I got 
>interested in the aplanatic gregorian. After running through the equations, 
>however, I discovered it was difficult to come up with a practical design. 
>Secondary sizes tended to be 50% or larger and/or the mirrors became quite 
>aspheric. My conclusion was that this is not an easy scope to make nor a very 
>useful design to build - better performance for less work out of almost any 
>other 2 mirror design. I suspect that's why it's not in R&V or many other 
>books.
>
See (400 mm f/16):

    http://users.rcn.com/rflrs/greg01-06.len
    http://users.rcn.com/rflrs/greg01-06.txt

Aplanatic with only 21.5 percent secondary size at 40+ mm field size.  
Or is there something more
I'm missing...

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