From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


Some designs use mangin mirrors (coated on the back) to create a different
abberation correction.  Some designs that resemble the Mak/Cass are the
Dilworth, and the Sigler (?), though these also use relay lenses to get the
focus outside the tube.  This allows one to use all spherical surfaces in
most configurations.  A similar concept is the old Questar design, I hear,
which allowed the beam to pass through the mak type corrector and bounce
off a "rear" silvered spot then back through to the focus. The
spot was painted over for protection. It was to avoid the Maksutov/
Gregory-Maksutov patent, I hear. Today, the Questar has an internal
secondary spot, like the usual Gregory-Mak.

To get better correction in the Mak-Cass, it's better to make a separate
secondary of a different radius than the corrector plate, or to allow the
focus to fall inside the tube, and use a diagonal mirror to shunt the
mirror to the side, like an unperforated cass. easier than relay lenses,
I'd say. Our club has a Fecker Celestar 6 which uses this shunted focus
design.  It is superb, optically.

ATMT series vol 1. "Optics", by A. Mackintosh has great designs
using variations on the Mak, and some Houghton designs, too.


Colin


-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of pdk
Sent: Friday, February 07, 2003 5:38 AM To: atm
Subject: ATM Need the name of an odd telescope design please.



At the St Pete Astronomy Clubs star party, a fellow observed with an
unusual 2 mirror scope.  It had a normal  "cass/mak/gregorian"
style look, however the secondary was a second surface mirror, using the
glass in front of the shiny side as a lens. The gentleman whom owned it
told me the name but several nights with limited sleep seem to have killed
the brain cells that stored that data.  Does anyone know what this is
called?  What kind of surfaces must be used?  It was a quite fine scope.

Thanks in advance,

PK

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