Re: ATM 11.5" mystery glass

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

Peter,

I have no idea of what they are worth. But as far as I could tell, they came
from a large store of World War 2 - era glass that was being worked on at the
US National Institute of Standards; there were lots of boxes of tank-turret
prisms (I think) and other stuff like that, that I was not interested in.

Yeah, these two would make an incredibly heavy refractor, at about 40 pounds
(would you in Australia call that ~3 stone, or ~18 kg?) each. Maybe they
intended to saw them in half, I ask rhetorically? I doubt it, it would have
been cheaper & to make them 1" thick to begin with.

I really do not know what they are worth. I just wanna make a 12" reflector.

Guy Brandenburg


PETER JOHN SMITH wrote:

> Guy,
>
> > My mystery glass has a companion piece, as well, same diameter, but a tad
> thicker. It has the following markings engraved on one of the parallel, clear
> sides:
> > Sk4 3979/# Opt. 7703 / Pos. 3/7
>
> SK4 is a more usual glass.  A higher refractive index crown. More demand for
> it too. But probably worth a bit worth more than the BaF4. They will,
> togeather, make quite a reasonable refractor BUT by no means APO. It would
> have to be about F:20 to perform reasonably.  Preferably about
> F:25. Would have to be a folded type for portability. I honestly doubt if
> they were originally really intended to make a refractor as the thickness is
> excessive. (about 2 inch ??? each - thats a big heavy lens at 4 inch) It
> sounds like someone may have paired them with the intention of making a
> refractor because they were available - even though they were really too
> thick.  Make a good camera obscura.The SK4 would also make a good MAK front
> lens. Better than the BaF4.
> I am interested in them but am in Australia. The freight and awkwardness of
> packing etc makes it far less attractive. What sort of money would you want.
> There will probably not be a much interest in the BaF4 by itself but as a
> pair they should be more interesting to people. All this has probably
> interrupted your planned start to your scope. Sorry about that. All the best,
>
> Peter Smith.