Re: [ATM] Banishing the secondary

[Mark Holm <mdholm@telerama.com>]

Enlarging a schiefspiegler isn't so simple.  Coma and astigmatism grow 
out of proportion to size.  4.25 inch is about as big as practical for a 
two mirror schief.

There are designs that use two mirrors and a lens.  The lens isn't 
especially tricky, according to lens makers.  (I'm not a lens maker yet, 
so I can't say.)  The two mirror and lens schiefs have been built up to 
about 12 inch.

The related Yolo design uses a warped or specially figured toroidal 
secondary mirror and can go to at least 12 inches.

Google on schiefspiegler and then on Leonard Yolo Telescope   (Art 
Leonard invented the design.)  If you Google on Yolo alone, you will get 
a huge number of references to the California county of the same name.

Mark Holm
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