Re: [ATM] Aplanatic Schmidt-Cassegrains with aspherical mirrors

["vladimir sacek" <vlad@copper.net>]

Michael Peck wrote:


> Oh, there are infinitely many ways to create an aplanatic SCT if you make 
> the primary conic an adjustable parameter.

Correct. I kept the primary spherical, which is not quite
clear in my post.

>...a dealer who probably knows more than he's allowed >to say assured me 
>that their new line of Ritchey-Chretiens *do* have two hyperboloidal 
> >mirrors...The one thing that still puzzles me a bit is that if >the 
>mirrors have the conics >of an RC the corrector plate has nothing to do 
>except hold the >secondary assembly.


I am also puzzled with what type of corrector that would be. One thing is 
certain, it can't be something difficult to manufacture. What comes to mind 
is a split decentered
meniscus. If the curvatures are relatively mild, it wouldn't
induce significant spherical and, if properly oriented, could
significantly reduce the RC astigmatism. The fact that
secondary holder doesn't protrude through the front side
seems to be indicating posibility of  such corrector type. It could also be 
relatively easy to make. Still, secondary mirror would have to be large - 
not much less than 50% - for near flat-field performance.

Vlad 


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