>In private email with Richard Schwartz, he commented that I might benefit
>from a 4-point flotation cell design.  I have a foggy (very) idea of how
>this works but...

Keith, as you would be aware, the mirror plane needs to be defined by 3
fixed points. For a four point cell imagine the normal fixed points for a
three point cell. We keep 2 of those points as locating points for the
mirror to the cell, but the third we replace with a beam. The ends of the
beam become the contact points for the mirror, while the middle of the beam
is the contact point with mirror cell. As to the actual 4 location points
on the mirror, I would guess they would be at 90 degree intervals at a 0.6
to 0.7 radius. Shouldn't be too critical with your mirror.

Andy Martyn
Canberra
Australia

Richard Schwartz sent me some sketches of various cells, including the
4 point cell. According to my program, the best 4 point cell has supports
at relative radius .509, and has about half the error of a 3 point cell.
I haven't put this on my web site yet, though, so don't look there!


David Lewis


>- - Who has tried this and with what success.

>My mirror is an 8" f/6.3 that's 1.25" thick Pyrex.

I used Richard's four point support design on my ten inch f/7 that's 1.25"
thich pyrex.  It works great!  No evidence of mirror warping due to cell
design at 600x.  Last weekend I transported this "not so transportable"
sonotube beast in my car for 25 minutes to a star party.  the tube sticks
out my car window and gets buffeted by 65mph air.  No loss of collimation!
Back home again and still collimation is good!

My mirror is bonded by RTV silicone to the cell, and I use/need no safety
clips.

About two months ago I posted my findings on this cell and describe it in
more detail.  If those posts don't help I'm happy to provide more details
and description.  It's a very simple mirror cell design that I made with
simple tools using aluminum and plywood.

I'm using similar concepts on a six point support of my sixteen inch, 1.6
inch thick pyrex mirror.  I'll post my findings in a few months on that cell
design.

Capt (Major select) Tom Krajci
B-52 Intelligence Officer
http://spur.barksdale.af.mil