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


If ever I was certain about how to do a planetary scope mirror, it would be
to flex it.  With that long an f ratio, you can flex it with 24 lbs pull,
with .009" wedge tolerance (that's a mile).  The cell would be much
easier to build than these multi-support cells, and the leftover error
(theoretical) from the flexing will be 1/285 wave.  In other words, what
you leave for error on the sphere will be about your only error, and it's
certain you can read errors of 1/20-1/30.

We have a 6" f/10.5, and a 7 f/9 and they are quite long.  Your 10 f/9
would be a huge scope.  Our club had a 10 f/10.  Needed a better design as
the currents in the mirror box were bad. Strictly ladder operation, and
hardly better than other smaller scopes.

f/8 would be easier.  You can get the obstruction down below 15% with an
f/8, and would not sacrifice anything.  Flexing it gives you 1/160 wave
error. I made an f/8.  Superb scope, too big to move around.   f/7 will
create 1/102 wave residual error, .005" wedge, etc, with 15%
obstruction. An extraordinary planetary scope, especially with a velvet
smooth sphere gently warped into a fine paraboloid.  The smaller scope will
likely be steadier, cheaper, easier to build, easier to use.

I use a 8 f/7 flex.  Superb.

I believe in this technology.

Colin




-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of pbunn
Sent: Monday, July 28, 2003 9:52 AM To: atmlist
Subject: ATM 10" F9 mirror thickness



I am considering a planetary scope 10"  F9 .

Is a 3/4" thick mirror going to be adequate or will it cause too many
problems? This is my second mirror.

Pat Bunn

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