Interestingly, a student at school mentioned that they heard old vintage lenses were radioactive especially the crazy Soviet ones. I’d never heard that one before. Working at a school means I have easy access to test equipment so I thought I’d put that myth to rest. You can imagine my astonishment to find it is not entirely unfounded!
This Zeiss Jena lens from East Germany circa 1960s contains thorium oxide which has a half life of pretty much forever. It was uncommonly used to produce clearer glass elements of less curvature to help prevent optical anomalies such as chromatic aberration. My readings show a plastic lens cap shields about 90% of the radiation. Only the back element is ‘hot’.
A bit more research on thorium reveals that it emits alpha particles which only travel a few inches through air and can’t readily penetrate skin. Still, radiation is cumulative so no source is a good source. In the grand scheme of things like x-rays and even flying in an airplane, this isn’t very much radiation. But I’m acutely aware of this lens now and can’t say I’m thrilled about it dangling around my waste LOL!
Out of 15 or so vintage lenses I tested, only this Zeiss Jena Flektogon produced a result. None of the Soviet lenses were hot probably because thorium wasn’t an economical substance to use. Still, it’s a fascinating discovery worthy of more research.