ATM Back Support for Large, Thin Mirrors

[Del Stanton <sdl20@pacificnet.net>]

>From a purely theoretical viewpoint it would seem that an
inexpensive way to support the rear of a large, thin mirror 
would be to use an array of diaphragms.  The air pressure 
would be regulated by a pendulum loaded regulator that 
would automatically increase and decrease the pressure 
(to balance the vector of the gravitational force that is 
parallel to the axis of the telescope tube).  Small clips, or 
an edge ring, would retain the mirror against falling forward 
as the telescope approaches the horizon.  These would 
also define the axial position of the mirror - the pressure 
being regulated so there was always a small "upward" force 
on the mirror - lightly holding it against the ring or clips.
>I do believe such a system was used on one or more of the 
large telescopes built during the 1960's.  It also used a 
mercury filled tube to provide an automatically compensating 
edge support.

It seems to me that this pneumatic rear support would be 
much easier to for an amateur to build than the typical 
multi-levered support system required to provide the large 
number of supports typically required for a large, thin mirror.
And the problems of stiction would be reduced if not eliminated.

Still - I would have each diaphragm support a pivoted triangle,
so the number of diaphragms required would be 1/3 the number 
of the support points.

And perhaps the edge support could also use a pneumatic tube 
with a second pendulum actuated pressure regulator.  The 
expense and danger of using mercury would be eliminated!

Del Stanton  - Burbank, California, USA (Near Los Angeles)

"sdl20@pacificnet.net"  (Lower case "SDL" followed by numeric "20")