[LargeFormat] Van Ripper didn,t know

[Richard Knoppow]

----- Original Message ----- 
From: "animal" <s.jessurun95@chello.nl>
To: <largeformat@f32.net>
Sent: Saturday, February 28, 2004 12:26 AM
Subject: [LargeFormat] Van Ripper didn,t know


> Just to be sure i mailed the M.Briggs article to Mr. van
Rippen.
> He was unaware of the radioactivity of an aero ektar!.
> Is there any more quantified info available that you know
of on these
> lenses?
> The reason is that i,m allready exposed to cosmic
radiation and would like
> to establish some sort of dosage received.
> Where would one go to have this tested?
> best regards
> simon jessurun
> amsterdam
>
>
  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.
  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.

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