Yesterday we mentioned Maksutov and Schmidt corrector plates used on
small mirror lenses and telescopes. The Maksutov is common on lenses of
about 500mm focal length and is a very thick meniscus lens with negative
curvature so strong you'd never miss it.
The Schmidt, on the other hand, looks like a thin, flat plate. The back
side is flat but the front side, even though it looks flat, actually has
a curve looking a bit like a flattened sine wave with a peak at the
center and troughs about 70% of the radius out to the edge. Very subtle
but it works to correct the spherical abberation of f/2 and faster mirrors.
Chuck Norcutt
Walt Wayman wrote:
> You could always just run a finger over it. :-)
>
> A reluctance to do that sort of thing is why I resorted to looking at
> the lens diagram when alerted to the possibility of a concave front
> element on the 50/2 DZ. Just looking at it, it's hard to tell.
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