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Guillaume,

The measurement of determining the curve is called a diopter. I don't know
the formula to determine the exact parabolic curve you may want, but Master
Craig might be able to point you in the correct direction. Mundanely he is
an Eye Doctor (I can't remember if he's an Optometrist, or an
Ophthalmologist). He ought to know those formulae or be able to point you
in the direction for them.

Lief

P.s. If nobody pipes up with his contact info, I think I know who might
have it. PM me in that circumstance. Hope this helps.
On Oct 13, 2013 8:10 PM, "Hall, Hayward" <[log in to unmask]> wrote:

>    Does anyone have references to period grinding of optical glass or
> metal, specifically concave mirrors.  I've see DaVinci's grinding machine
> (too difficult to produce), various post-period techniques, and sphere
> production for eyeglasses, but nothing really relating to the large concave
> "burning mirrors" described both in antiquity and in late period.
>  Birringuccio talks about casting them but really doesnt go into how to
> produce the parabola.
>
>  I'm currently employing techniques used by current Amateur Telescope
> Makers however, while primitive, I don't know their origin.
>
>  Thanks.
>
>  Guillaume
>
>