On Wed, 14 Dec 2005 03:27:50 GMT, lid
(John Savard) wrote, in part:

And I find that
Petzval
-based telescopes are becoming common *now*
because a patent has expired... U.S. patent 4,400,065, from 1983...
issued to one Al Nagler. If it's *his* idea, it probably _is_ a good
one!

Oops!

Apparently, it's a cheaper way to get to f/4 than to go apochromatic...

John Savard
http://home.ecn.ab.ca/~jsavard/index.html
http://www.quadibloc.com/index.html
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