Re: ATM 11.5" mystery glass

["PETER JOHN SMITH" <pjifl@bigpond.com>]

Guy Brandenburg wrote :-


> 
>   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!



I have since had time to check further on BaF4.  

30 seconds after the last post I had to be out the door moving fast which
explains the very short and inadequate and somewhat terse note.  Sorry for
that.

Now I have had time to check, partial dispersion information places this as
far less interesting from the point of view of APO design.

It will produce a normal refractor but of slightly less than normal
performance unless paired with another very expensive glass.

While unusual for the purpose, it will produce a good MAK - especially in
conjunction with another small correcting lens. Of course a lot of
generating will have to be done. If no one else will, I will work up a MAK
design for anyone who wants to use this glass.

A pyrex blank will produce a better mirror for a Newt.  In fact a 1 inch
piece of plate glass well mounted would be just as good.

It seems like an incredible waste of a piece of optical glass to simply
turn it into a mirror.

If I was closer, I would certainly be immediately swapping a piece of pyrex
for this piece of glass.

Of course, this supposes that it is correctly marked and identified.  An SG
measurement would be sufficient to confirm if some doubt exists.

At the very least, if it is turned into a Newt, engrave on it the glass
information so someone someday can rescue it for a better purpose. Any
piece of optical glass 11.5 diam and two inches thich is worth a reasonable
amount.

All the best,

Peter Smith.