[ATM] Working with Large Thin Mirrors

["Peter" <peter@kitgear.com>]

Hi,

Aperture feaver has set in really bad so I've decided to get back to work on
my 25" x 1" thick mirror. I'd like to ask for advice how is best to proceed
to minimize astigmatism. I've polished just enough to see that I do have
some astig which I'd like to remove before proceeding.

Here is the basic info so far:

- Mirror is 25" OD plate glass at f/4.8 and 1" thick at the edge
- The tool is a sub-diameter ceramic 3/4 size (19") and 2.25" thick.
- The mirror was until now supported on the bottom with thick carpet
throughout all of the grinding and polishing
- Polishing pads are being used
- The back of the mirror has not yet been ground flat

Some questions I have before proceeding are:

1)	Should I grind the back side? If yes then how would I do this for such a
large mirror or could I make it a shallow sphere?

2)	Is it best to go with a full size tool Vs sub-diameter?

3)	Should I work it with the mirror on top to better support the glass?


Please let me know what you think is best.

Thanks,


Peter


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