ATM Tweaking Commercial Mirrors

["Bennett, Thomas D" <thomas.d.bennett@lmco.com>]

Hi ATMs,

Thanks for all inputs on the Foucault frustrations I was having. Apparently,
leaving the mirror in a room which was thermostatically controlled all day
and turning off the control while testing in the early evening caused a room
temp drop and the relatively hot mirror changed shape as it cooled during
the testing. Did much better after leaving thermostate off all day and then
testing.

After Foucault testing several commercial mirrors manufactured from late
'70s to early '80s - I've noticed that  they are all undercorrected by
between 1/2 - 1/8 wave. Is this reasonable or am I doing something
systematically wrong? How difficult would it be for a relative newbee to
make a pitch lap and tweak these mirrors into the 1/15 - 1/20 wave range?
I've got the testing process down pretty well but I'm a little hesitant to
alter a good mirror in order to make an excellent mirror. How much
additional parabolizing (time wise) will be required to shave off this
minute amount of glass and am I likely to create other problems on the
mirror figure? I'm guessing this final tweaking of the figure must be
difficult - otherwise these commercial vendors would have done it.