Re: ATM Active mirror figure correction?

[iss@pvtnetworks.net]

Lawrence Sayre writes,

>Is it possible to glue a small "swivel level" pad onto the dead center
>of the back side of this mirror

> and then torque a nut
>on the swivel level bolt to literally pull this thin plate glass mirror
>into a good parabolic curve?  Or would this induce loads of stress
>related astigmatism, or worse, shatter the mirror?

I had a 24" f4 scope which as originally built, had a 1/2 wave smooth
hill over the central 50% of the diameter. It was supported by an
18 pt flotation, and had a 4" hole in the center, the radial support was a
threaded tube thru the hole with a retaining ring not quite touching
the mirror in normal use. The nut & tube were insulated from the glass
by a thin nylon washer & sleeve.

As an experiment I did a Ronchi test on Polaris while carefully tightening
the retaining ring, this pushed the center of the 1 5/8 thich mirror
down relative to the edge. It was actually possible to eliminate most of the
'hill' with a moderate amount of force on the center; unfortunately the
star image became triangular shaped because of the 18 point flotation.

I did not try a ring support, also the amount of pressure would be variable
with elevation. The mirror was refigured to correct the hill, for me that was
an easier solution..:)



Andy Saulietis / ISS Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designed mount/telescopes & Machine work
CCD filter wheels & other custom accessories
39 Silver Fox Trail
Cloud Country Estates
Mayhill NM 88339
505-687-3067 Voice
505-687-3021   Fax
e-mail: iss@pvtnetworks.net
32 54 13 N  105 31 44 W 7300' elev