[ATM] Mirror Regrind.

[Hugues.Laroche at ses-astra.com (Hugues.Laroche@ses-astra.com)]

Buon giorno Marco,

> the 12in F3.3 (paraboloidal) Mirror <SNIP>
>I tried a 3in flat with it and do not
>like seagulls.

Don't you have a friend who could borrow you a Paracorr
or similar coma corrector, just for the trial? At f/3.3
it would not take out all the the coma but could still give
good results, at a fraction of the cost+pain+risk of a mirror
regrind.

>F8 plantary scope would be nice

Man, you then have plenty of glass to grind off!

>Here's the dilema: Do I
>1/  Regrind the F3.3 face
>or
>2/ Flip it over and grind the flat rear face?

I would propose a 3rd solution: you sell this mirror
for a decent price to allows you to get a new blank
pre-generated at f/8. I even might be interested.

If you are absolutely to regrind it I would choose option 1),
as Bob May said, use a small metal tool to get the edge down
(down forget to bevel very much or you might take off big
chips from the edge). When you near your target curve, make
a plaster + tiles tool and get the things spherical.
BTW you did not say what material is the mirror made of?
With the military it may well be a special stuff like zerodur
which would give you hard time to grind/polish.

Happy ATMing... think twice or more before settling a decision!

Hugues




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