[LargeFormat] Van Ripper didn,t know

[Richard Knoppow]

----- Original Message ----- 
From: "Michael Briggs" <MichaelBriggs@Earthlink.net>
To: <largeformat@f32.net>
Sent: Saturday, February 28, 2004 1:48 PM
Subject: Re: [LargeFormat] Van Ripper didn,t know


>
> On 28-Feb-2004 Richard Knoppow wrote:
> >
>
> >   I suggest contacting someone at George Eastman House
and
> > also Rochester Institute of Technology. By memory, GEH
had
> > to dispose of a number of lenses in its collection
because
> > they were radioactive.
>
> I doubt that photography curators will be knowledgable
about the physics and
> biology have high-energy radiation. The area of expertise
is Health Physics or
> Radiation Safety.
>
> >   Some of the first rare-earth glasses contained some
> > Thorium because it gave glass with advantageous
properties.
> > It is sometimes stated that the Thorium was an
untentional
> > impurity in Lanthanum glass, but it was a delibrate
> > addition. I don't have the patent numbers for the Bureau
of
> > Standards glass although I have the patents somewhere.
The
> > formulas for several glasses are in the patent and show
the
> > use of Throrium to obtain high index, low dispersion
glass.
> > The patent is not in Kingslake, I'm not sure where I
> > orginially found it.
>
> The patent number for the Aero-Ektar is in Kingslake's A
History of the
> Photographyic Lens: Aklin, US 2,343,627.  His discussions
on the new glasses of
> Morey and Kodak is a bit misleading in that he calls them
Lanthanum Crowns and
> doesn't mention that all of these glasses also contained
thorium, though he
> does mention this fact in the Nature article that he
references, Kingslake and
> DePaolis, Nature, vol. 163, pp. 412-413, 1949.
>
> You probably got the glass patents from me.  They are
Morey, US Reissue 21,175
> and Eberlin and De Paolis, US 2,241,249.
>
> It would be very interesting to find the patents (if they
exist) for other
> lenses using thorium glass, e.g., some Xenotars, a
screwmount 50 mm f1.4
> Pentax Super-Takumar, the pre-AI Nikkor 35 mm f1.4,
Repro-Claron, .....
>
> --Michael
>
  I didn't mean the patent for the Aero-Ektar, I have that.
I mean the patent for the rare-earth glasses from the NBS. I
have it but finding it on a zip disc filled with patent
numbers would be time consuming without the number. Its in
one of my books on optics, I just don't remember which one.
  I doubt very much if Thorium was used in any consumer
lenses at all. Lanthanum was used in lots of them but
Lanthanum is not radioactive. Most of the radiation from
Thorium is alpha particals which die away quickly with
distance.
  One problem with determining the makeup of optical glass
is that its usually proprietary. That is one reason the NBS
patents are so intresting. Most lens patents do not indicate
the full info on the glass anyway. They usually give the
idex and Abbe number (v number) but not the anomolous
dispersion. This makes it difficult to analyse apochromatic
designs with a computer program. One can guess at the glass
but only that. For instance, in LensVIEW many well corrected
lenses show up as partially corrected, and apo lenses show
up as undercorrected or as achromats because the glass types
are not actually known and were guessed at in compiling the
program.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com