Re: [ATM] Another flat-field anastigmatic aplant

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

vladimir wrote:

>Some intermediate arrangement with less astigmatism is possible, but 
>somewhat smaller
>primary opening doesn't seem to be be worth sacrificing near-perfect field 
>correction.
>One thing I would do is try to optimize a "small secondary arrangement" so 
>that
>vignetting at the tertiary reduces to a minimum possible. That would be as 
>good as it gets,
>at least as far as I can see.
>

Hmmm... I tried changing both the f/# and the distance of the
focal plane behind the primary.  For any reasonable change I
tried, the unvignetted diameter of the central hole minus the
unvignetted diameter of the secondary at optimal performance
ended up being quite close to 19.5% of the primary aperture
(minus zero, plus a millimeter or so).
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