Re: [ATM] mirror cell design

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Jerry B. Hillman" <JBHillman@ev1.net>

> Hi All,
> Can anyone point me to a version of Plop that supports 54 point cells.  I am
> currently using a 27 point cell but am having difficulty with astigmatism.
> During one test session I will have perfect, astigmatism free results, then
> the next time I set it up, I will have astigmatism.

Jerry,

If I recall correctly, you have one of those thin mirrors, yes?  If so, (and if
it behaves like Ron's 22" x 3/4" thick F/6) you problem probably lies more with
edge support than back support.

Unfortunately I can't offer any suggestions, other than what we tried and didn't
work out so great.  Nylon or wire slings didn't work so well.  Single posts or
posts with two 'swivel supports didn't work at all.  Gluing the mirror to the
cell was a complete failure!

To date, the 'best' results have been from a thin steel sling, with several
types of adjustments.  (Tip - Tilt - Piston).  We've also glued some "Helper"
springs to the back of the mirror in an attempt to 'pull' out the astigmatism.
(Previous sentence said in a some what serious, but mostly humorous tone!)
Honestly, the helper springs have helped on an occasion, but they are NOT
consistent.

I'm trying my best to talk Ron into drilling a 3/4" diameter hole in the middle
of his mirror.  The idea is to let the cell support the back of the mirror, and
a Post up the center to provide lateral support in place of the sling.

Anyway, just something to think about.

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge



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