Hello again, Thomas.
>So you are saying that some older radioactive-glass
>lenses may go yellow, while others of about the same
>age will not?
AFAIK, the use of radiactive lens elements (thorium, lanthane, etc) were
relatively common on photographic lenses from the late 60s-early 70s, in
order to achieve higher performance -- like the earliest Zuikos 50/1.4 and
55/1.2, several Pent*x screw-mount lenses and the Russian Industar-61L/D (a
*very* sharp Tessar-like 55/2.8), among others.
But some glass tends to go yellow when exposed to radiactivity (either
external or generated on the lens itself). Quoting a Russian book on
Optical Instrumentation: '...We note that series 100 glass -those with the
numerical index varying from 100 to 199- are non-browning formulations;
this browns less of all when exposed to nuclear radiation...'. On a
catalogue of Russian-made glass, most types have a non-browning version:
K8/K108, BK10/BK110, LF5/LF105, and so on.
I think that yellowing depends on the lens' formulation: if it has a
radiactive element *and* uses standard ("browning") glass, yellowing should
be noticeable after several years -- this time ought to be quite similar
for any lens of the *exact* type and formulation. Some Pent*x lenses of
circa-1970 are famous for yellowing.
On the other hand, lens' formulation is usually changed within production,
so you may find two samples of a lens of not-too-different age, one of them
yellowing but not the other -- radiactive elements were commonly discarded.
Maybe a lens without any radiactive elements, but exposed to unusually high
radiation levels, would show yellowing. And I haven't heard of any I-61LD
yellowing... yet!
Hope this helps,
...
Carlos J. Santisteban
<cjss@xxxxxxxxxxxxx>
<http://cjss.galeon.com>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|