ATM - Figuring by Cell Tuning

[Richard Schwartz <richas@idt.net>]

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Disclaimer:   The following reply is of no commercial interest and is
offered
with the intent that no running dogs of the wall street capitalist
ruling clique
profit herefrom.  Nothing herein is to be construed as an endorsment of
any product or ideology, including the writer's.
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The deformation of a mirror in a flotation cell depends on the forces
applied
by the cell to the mirror.   These loads, in turn, depend on the
elevation
angle of the telescope.   If the telescope is pointed close to the
horizon,
all of the load forces on the mirror flotation points vanish.   So it
would not
be possible to apply a figure correcting load.

Our best bet is to start out with a good quality mirror, and then float
it so
as to minimize the deformations when it is under maximum load (telescope

aimed straight up).

I see a common fear in newcomers: they are afraid of parabolizing.
Most of them feel comfortable polishing a spherical surface, but the
esoteric nature of the polishing strokes and the interpretation of the
foucault test readings fills the heart with terror.   Let it be known
that
there is no magic going on.   Once you get the hang of it, you will
know when your figure is right.  And the simple truth is that any kind
of conic figure -- ellipsoidal, hyperbolodal, or the xombwongi
mbossangu curve -- are all equally easy to do simply by scaling
the foucault test readings.

What I miss is a good old PPC stuffing party.   That was when
we would meet at the clubhouse stuff about 8000 journals into
their envelopes, paste address labels on the envelopes, and then
hack on our HP-41 calculators and get high on diet Pepsi until
dawn.    PPC was truly a non-profit operation: we never made
a profit.   We did it for other reasons.  Those of you in the
Corvallis, Oregon, area may have heard of us.

. . . Richard



Date: Thu, 21 Jan 1999 20:01:15 -0500 (EST)
From: Ken Lowther <s0109366@cc.ysu.edu>
Subject: Re: ATM Anna Moore Telescope Mirror Surface Deflections
(Internet
Shortcut)

On Thu, 21 Jan 1999 lewis@eecg.toronto.edu wrote:

> found that an optimized 9 point cell can go up to 22" in diameter with

1/128
> RMS tolerance on the surface, i.e. about 1/16 wavefront P-V on the
reflection.

Would there be any merit to the idea of using your zone readings from
testing and tuning your cell to the actual figure?  If it's going to
flex,
why not have it flex in a "helpful" way.

Ken Lowther
s0109366@cc.ysu.edu
Youngstown, Ohio  USA