Found out Canon's old FD lenses have radioactive glass in them

Was reading a forum last night while waiting for glue to dry on a shutter rebuild and stumbled onto a thread about thorium in Canon FD 50mm f/1.4 lenses from the 1970s. Someone posted a Geiger counter reading showing the rear element puts out like 3 times background radiation. Has anyone else run into one of these hot lenses and had to handle the yellowing?

3 comments

3 Comments

carr.luna13d ago

Have you tried the UV light trick on one of those yet? I picked up a yellowed 50mm f/1.4 a few years back from a thrift store for almost nothing. Left it in a sunny window for about two weeks and the yellowing faded out pretty good. The thorium thing creeped me out at first but honestly I figure as long as you aren't grinding the glass into dust and snorting it you're probably fine. It's wild to think those old engineers just mixed radioactive stuff into lenses like it was no big deal though.

the_daniel12d ago

Honestly I gotta push back a little on this one @carr.luna. I've seen enough people claim the UV trick works but I've also seen tests where the yellowing came back after a few months, especially in humid climates. Plus the whole thorium thing is a bit more dicey than folks let on. Those lenses emit radon gas as they decay, and while it's low level, having one sitting on your desk or in your bag next to you for years is a different story than just handling it occasionally. I'd rather just hunt down a clean copy without the radioactive glass, even if it costs more.

the_sage13d ago

Found an old Takumar 50mm f/1.4 at an estate sale last year with that same yellow tint, and a week on the windowsill cleared it right up. @carr.luna your point about not grinding the glass is exactly what I tell people who get spooked by the thorium. Honestly I think the whole thing is more scary in theory than it is in practice.