I have the radioactive element from a 50/1.4 right in front of me (ok,
a couple of feet in front of me, and I'm not about to start carrying it
in my pocket as a good-luck charm), and it sure looks to me like the
GLASS is yellow, and NOT the coating. The edges are yellow, which
probably shouldn't be true if it were just the coating, and if you look
through the lens obliquely, it looks more yellow since you're looking
through more glass. If just the coating were yellow, I would think
this effect would be quite small. It is well known that
thorium-containing glass was used in camera lenses, and I believe that
in the Zuikos in question, it is the GLASS that is both radioactive and
changing color. The color change is almost certainly from alpha
radiation (He4 nuclei) which would be absorbed by the glass, whereas
the beta and gamma would go through the glass.
I think I remember reading that the production of thorium-containing
lenses was stopped due to health hazards to the workers who made it,
which wouldn't surprise me in the least.
And to answer another question, the only Zuikos known to be radioactive
are the silvernose 55/1.2's, with 2 radioactive elements, and the very
early 50/1.4's, with one. These are also the only known Zuikos to
yellow. If your 55/1.2 is not a silvernose, then it's almost certainly
not radioactive. There are silvernose 50/1.4's that are not
radioactive though, and the SN of the change has not been determined.
There are no radioactive 50/1.2's, and no known 50/1.8's.
Mark
Ahhhhh Ha...... Exactly!!!! Just posted re this fundamental issue.
ONE: degradation is primarily in the organic binder substrates of
the
coating NOT the inorganic matrix of the glass. TWO: whether induced
by ionizing radiation of 'radioactive decay', HEAT, cosmic radiation,
etc., you see the effects of degradation in the same end results.
Given a constant level of ionizing radiation (UV, radioactive, cosmic,
visible light spectrum, whatever......) the degradation rate of the
coating will vary greatly depending on ambient temperature AND
HUMIDITY. All of this is additive. As you appropriately remind, the
differing degradation of the same lens reflects changes in additive
contributions from the environment. Further, since the exterior of the
lens ( the coating surface) has greatest exposure, virtually all of the
observed changes are limited to that molecular level, NOT the glass.
Enuff....
Bill Hunter
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