I recently acquired a Canon A-1 film camera with an FD mount and I'm looking for some guidance on which lenses to use that do not contain thorium. I've done some research and learned that some older lenses were made with thorium glass, which can be mildly radioactive and pose a health risk if handled improperly.
While I understand that the risk is relatively low, I'm still a bit nervous and would prefer to avoid thoriated lenses if possible. Can anyone recommend some Canon FD mount lenses that do not contain thorium? And if there are any lens technicians or experts who can provide guidance on identifying thoriated lenses or confirming whether a lens is safe to use, I would greatly appreciate your input.
Thank you in advance for your help!
I spent 3 min reading about thorium. Its relatively harmless. Most thorium exposure occurs through dust inhalation; some thorium comes with food and water, but because of its low solubility, this exposure is negligible. Thorium exists in the earth's crust. If you live in India or Brazil, you might be at risk for higher exposure. Another possible source of exposure is thorium dust produced at weapons testing ranges, as thorium is used in the guidance systems of some missiles.
Armed with this information, you can gauge your risk for exposure and determine of handling lenses that might contain thorium is going to place you at appreciable risk for actual health risks beyond the chances you take of losing your life each day you walk out the door of your house. > Seriously.
You could also play it safe and buy a new camera. One whose lenses might not be coated in thorium. Now you don't have to be scared to pick up your camera. Problem solved. 👍
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I wonder if it's similar to uranium glass from pre-WWII or even lead paint used on Pyrex/Corelle? (Basically - yes, it's there, but you have to go out of your way to get any real exposure from any of it.)
thorium 232 is an alpha emitter. Paper can block alphas, assuming that the thorium elements are inside the lens, there should be no issues with radioactivity.
Plutonium, another alpha emitter, is only dangerous if a particle is inhaled and stays in intimate contact with lung tissue.
(I won't tell you my current job which makes me have to be knowledgeable about nuclear materials.)
Yes, but it is not much and as you say the short half life means it goes away quickly and the fact that thorium 223 does not decay very quickly means that there is very little beta to worry about.
Different people have different risk thresholds BUT thorium glass in a lens is something that really should only be on your list if you worked in a processing plant when those were made. Thorium is used in many different products including a lot of consumer products of years past that had high power vacuum tubes with thoriated filament construction.
Stephen, the uranium glass is "hot" enough to be easily readable with a radiation detector but unless you plan to sleep with it like a teddy bear it isn't a concern. A lot of WWII era high power transmitting tubes have "uranium glass" in the seals area to withstand high temperature. Most humorous is people scared of tiny little voltage regulator tubes because they have the internationally recognized symbol for radioactivity on them. There is a tiny amount of material used to ensure the gas properly ionizes in a cold/dark environment but the only hazard would be to break one and then snort the contents.
I would be far more concerned about wearing bluetooth devices in my ears or walking around all day with a phone glued to my head than any possible exposure from a lens. A short visit to high altitude areas in beautiful Colorado or other rocky mountain states will provide more exposure and I am looking forward to my next visit to the high mountains. And I am pretty sure if I knew the entire environment of pretty much any commercial processed food, I would soon be anorexic!
I am about to leave to shoot a post-season soccer playoff match using a 1DX III body with an EF 200-400 1.4X for the first half and a 400 f2.8 for the second half after sundown and the big hazard with those would be dropping one on my toe 🙂 That is a hazard with some actual likelihood of being actualized.
I think it's generally agreed that thoriated lenses are a pretty low risk to health, unless you hike around with them in a backpack, and even then it's not high. My concern would be the yellowing that the radiation causes over time, and even that is curable. Certainly don't break them and inhale the dust, that would be bad.
Media Division did a video about FD lenses, and covered the thorium issue pretty well, so this might help: https://www.youtube.com/watch?v=v8Il_l3tu6Q&t=3s
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