Re: ATM 11.5" mystery glass

["Guy F. Brandenburg" <guyfbran@erols.com>]

PETER JOHN SMITH wrote:

> > Guy Brandenburg wrote: "Last night I started rough-grinding a piece of
> glass "inherited" from the WW2-era stocks of the old National Institute of
> Standards. It's 11.5" in diameter, 2"  thick, and it has some interesting
> data written on the side with grease-pencil and  engraved into one side of
> the glass.  Anybody care to decipher them? They are written in a European
> hand (1's with a  pronounced upward zig, crossed 7's, etc)  Here goes:  BaF4
> - Z4135 Opt 7702 / Pos 2/38  I suspect the BaF4 means a type of glass
> containing Barium Fluoride, and the 2/38 may mean February 1938, but the rest
> I really cannot guess at. "
>
> PJS responded: "BaF4 is a relatively unusual light flint glass. It could
> certainly be used as the flint in a refractor.  In fact I would guess it
> could be used in something approaching an APO design. Have no time at the
> moment to investigate further. BUT UNDER NO CIRCUMSTANCES SHOULD YOU WASTE A
> VALUABLE PIECE SUCH AS THIS ON A REFLECTOR."
> Peter Smith.

  If it's all that valuable, does anybody actually have the time and energy to
turn it into an achromatic doublet or APO triplet, and want to trade for a
similar-sized piece of Pyrex? I know that such a project is way beyond my
capabilities; I just want to make a nice, cheap, simple, medium-focal-length
~12" reflector!

Guy Brandenburg