8" diameter flat mirror. Made of glass-ceramic
low-expansion material, 1:6 thickness.
Interferometric report (included, in Russian)
indicates RMS wavefront error at 1/40 wave, with
maximum local error better than 1/15 wave, and
max astigmatism of 1/9 wave, and max Peak-Valley
local deviation of better than 1/6 wave.
Aluminized 95% in excellent condition.
Use it to:
1) test optics.
2) fold a refractor (coude or elbow).
3) make a siderostat (I did this, using a 4" fluorite APO)
as shown on page 396 of Texereau ("How to Make a Telescope")
second edition (Willman-Bell). Also Sky&Tel, July 1970, p46.