Everything You Always Wanted To Know About Radioactive Lenses

We think of radioactive material as something buried away in bunkers with bombs, power plants, and maybe some exotic medical equipment. But turns out, there are little bits of radiation in the water, our soil, bananas, granite countertops, smoke detectors, and even some camera lenses. Camera lenses? A few decades ago, camera companies added rare elements like thorium to their glass to change the optical properties in desirable ways. The downside? Well, it made the lenses somewhat radioactive.  A post by [lenslegend] explains it all.

Exotic elements such as Thorium, Lanthanum and Zirconium are added to glass mixtures to create the high refractive indexes necessary in sophisticated lens designs. Selection of premium quantities of glass from the large glass pots, stringent spectrophotometric tests after stress and strain checks provide the valuable raw glass for ultimate use in lens elements.
Konica Hexanon Lens Guide, Konica Camera Company, 1972

According to [lenslegend] the practice started in 1945 with Kodak. However, by the 1980s, consumer distaste for radioactive things and concern for factory workers ended the production of hot camera lenses.

Thorium is the most abundant radioactive material on Earth, but it eventually turns into lead. The half life, however, is just over 14 billion years, so your lenses probably won’t turn to lead in the closet.

While thorium only releases alpha particles, in doing so, it becomes radium which will then, eventually, release a beta particle and becomes a different isotope of thorium which later decays to several other elements until it becomes lead. When beta radiation slows down it can produce X-rays or gamma rays.

The saving grace, according to [lenslegend], is the amount of material is small and so is the radiation. However, apparently inhaling or ingesting radioactive glass dust can be a problem. Alpha particles can’t go very far through your skin. But once inside your body, they can be hazardous. This is also why radioactive glass shouldn’t be used in eyepieces.

So if you are wanting to take apart vintage lenses, you might want to be aware of this. A Geiger counter will tell you if your lens is hot. However, if you don’t have one, you can look for yellowed glass. Radioactive decay could also cause hot spots on digital cameras.

In the consumer market, it doesn’t look like radioactive lenses are still a thing. However, there are some military lenses and it is conceivable that in military or industrial surplus you might find radioactive glass.

Glass may have been the world’s first engineered material, but it is still very useful. Even today, there are new techniques for creating with glass being developed.

42 thoughts on “Everything You Always Wanted To Know About Radioactive Lenses

    1. My guess is that these concerns are mitigated by several factors. First, most alpha and beta particles are absorbed in the glass itself and never make it out; second, if the high index lens is not the last one facing the film, all alphas and betas will be absorbed in any other lens in the way. However, some K-shell x-rays produced by the high-Z elements will be energetic enough to pass through any glass in the way, so could be a problem, but unless the source is really hot, any particular frame of film probably doesn’t spend a lot of time facing the lens to fog it all that much.

    2. So with film you’re constantly changing out which frame is behind the lens. I have a few surprisingly radioactive lenses (as in, I could see the increased gamma levels over background from outside the box they were shipped in). I make sure not to leave them mounted on the digital camera when not in use. Modern sensors are many orders of magnitude more sensitive to light, and accumulated radiation damage is more permanent than with film where you might just fog a picture or two.

      NASA has some papers on damage thresholds for CMOS imaging sensors, and I’m not that worried given the length of time required to create a meaningful increase in noise, but it is a measurable effect.

    3. They’re not very radioactive (I have a 58mm canon FL lens, a few Giger counters – and a gamma spectrometer…).

      Putting the Giger tube about where film or a sensor would go reads about 10 times background dose. And filtering out alpha/beta with aluminium doesn’t reduce this much for my meters. Interestingly 1mm of lead halves the dose, which indicates there’s a goodly amount of gamma. Not from the Thorium, but from some of the stuff it breaks down into:

      https://www.gammaspectacular.com/blue/th232-spectrum

      Winding up the ISO all the way on my R5 to truly silly levels shows the occasional flash. Unless a very thick lead shutter were used it would slowly expose film. Can’t quantify how fast it would do this but imagine it would take a very long time as it doesn’t seem to be reported as a significant issue. While it would fog the frame that’s waiting behind the shutter, there’s not much extra distance to the film canisters at the sides so a little would sneak in there too.

      Randomly for comparison, the Fl lens I have is about the same activity as a friends collection of Uranium glass tableware. Probably a bad idea to keep film in one of those glasses!

      1. I collect uranium glass, so I’m getting a kick out of this. :)

        If you really want something “hot”, look at Fiestaware. I have one of the old “radioactive red” plates in a kitchen cabinet with my other plates, and not only does it throw about 10x as much alpha as my hottest uranium glass, it throws enough gamma for my Geiger counter to read outside the cabinet.

        The amount of radioactivity from one of these lenses is nowhere near enough to fog film.

    4. Wouldn’t it also depend on the amount of radioactive material in the lens itself? A 100% thorium lens would have a different radioactive output than a glass lens with 1 PPM of thorium in it.

    1. This is an issue where optical fibres (hard clad silica) are used in high radiation environments too. The effect can be somewhat mitigated/reversed by heating the glass to a few hundred degrees Celsius (well below it’s transition temp).

  1. “Somewhat radioactive” is still a massive overstatement and misleading.

    As the article shows, the guy measures 79.5 microsieverts per hour of radiation coming out of the glass. Then he goes to show that putting simple eyeglasses between the lens and the meter reduces this by a factor of ten. However, he lefts without mention that the normal background radiation level is about 700 microsieverts per hour out of natural and man-made sources.

    People just don’t recognize that we’re all bathed in ionizing radiation all the time. Go to a beach, pick up a pinch of sand and eat it. Now you have more alpha emitters in your body than you would ever get exposed to out of a camera lens. Washing your hands or not keeping the lens in your pocket etc. are just senseless paranoia.

    The only problem out of these lenses is with the handling of the raw materials at the factory, where radioactive contamination can be concentrated to dangerous levels.

    1. Or, as the guy himself quotes from a paper: “These ratios are so close to zero that the conclusion drawn in this thesis is that there are no radiation related health hazards involved in the usage of any of the camera lenses measured.”

      But then he says:

      “To avoid elevated radiation exposure – store the radioactive lenses as far away from yourself as reasonably possible. If you have a choice, do not keep them in the bedroom or locations where they are close to humans for prolonged periods. Even though the exposures are small, they all add up over time.”

      I mean – what? No. It does not “add up over time”. Your body is evolved to deal with massive amounts of ionizing radiation and repair the DNA damage, and your immune system is destroying cancerous cells all the time. He’s simply propagating the myth that radiation exposure is cumulative at all levels, known as LNT – Linear No Threshold model.

      https://en.wikipedia.org/wiki/Linear_no-threshold_model

      This assumption has actually caused the deaths of millions of people by over-reactions for radiation safety. People displaced from their homes, ostracized and rejected by their communities, driven to alcoholism, depression and suicide. It’s highly irresponsible to keep propagating the lie.

      1. Oh my, these days just pointing out that LNT is factually a politically-driven fraud and citing an article that backs this up on Social Media (yeah Wikipedia is Social Media) will just get the article banned (censored). Shhhh… keep the truth to yourself. Speak softly and in private. This is America.

        1. Is it possible that too many people complaining about LNT are also pushing hormesis nonsense as well?

          It is possible that “radiation past a certain threshold is dangerous” is true while “some amount of radiation is beneficial” is not true. I don’t think any chemist would argue that cyanide is healthy or beneficial, but it also isn’t harmful below a given amount. An apple seed won’t kill you.

          Unless you are very allergic to apples.

      1. Also don’t tell them that the LNT model of cumulative effects of ionizing radiation has been discredited ages ago.

        Radiation exposure doesn’t “add up” at low levels. Keeping up the myth is now bordering dangerous pseudoscience, because it’s ruining peoples lives and keeping us from using one of the best forms of energy to combat climate change.

        1. Same with elevated levels of sodium in your diet will always cause heart damage, high blood pressure etc. Not happy with the slapdash 50 year old study on it, the CDC did a long term, rigorously scientific study with a large number of participants and found that human biology can tolerate quite elevated sodium levels. it’s only people who have a malfunction of the process that automatically maintains proper blood sodium levels who need to watch their intake. The study also found that *too little* sodium was greater concern for heart disease.

          Seems like common sense since nerve impulses and muscle contractions rely in part on sodium.

          The TL;DR of it appears to be that any individual’s issues with sodium are *individual*. If you’re going to develop sodium sensitive hypertension, you will, and consuming less salt will do little, if any, to stave it off, but not eating enough can cause problems that have long been blamed on too much.

          The industry built upon that early 1970’s study have been trying to “debunk” the CDC study ever since its release.

          But in the short time since then the CDC has been bowing to politics, waffling on their 3,000 subject, randomized, controlled trial of common surgical masks VS Influenza found they provided little, if any protection. But they’ve found all kinds of bordering on magical reasons for the masks to protect against SARS-CoV-2. They focus all on droplets and aerosols, dismissing the free virions (individual viruses) that can sail right through the mask pores much larger than the virus and the big leaks around the edges all these masks have. Aerosols, droplets, free virions, all will blow out and be drawn in past the edges.

          Then the CDC in April said it’s time to end the “hygiene theater” spraying disinfectants on everything hasn’t and doesn’t do a thing to protect against the SARS-CoV-2 virus. But the media and governments have turned a blind eye to that bit of sound advice.

          And now I’m going back to bed because my reaction to the Moderna vaccine is doing its best to emulate a common cold, in reverse order.

    2. Normal background radiation is around 0.1 uSv/h, not 700. I just returned from a tour from Chernobyl and the highest dose rate I measured there was 20 uSv/h, so 80 uSv/h from that lens is quite high. Nevertheless, it’s unlikely to be a health hazard unless you ingest or inhale it.

      1. Nope.

        Average exposure in the US is 6.24 milliSieverts per year. A milliSievert is 1,000 microSieverts. There are 8760 hours in a year which makes it 712.3 microSieverts per hour.

        The normal background levels vary wildly. A wooden house away from sources of radon will have minimal radiation, whereas a house built out of concrete will send your geiger counter buzzing.

        1. Oh, I did a decimal point shift twice – it’s actually 0.7123 uSv/h

          Still, the guy is measuring 0.674 uSv/h at a distance of 45 cm which is perfectly average. Not dangerous. People live in places which get 20 mSv/a or 2.3 uSv/h which is over 3x the amount you get from the lens.

    3. The guy is claiming 0.246 uSv/h as “twice the background level”, which would suggest that the background level is at 1 mS/a which is actually 1/6th the average background radiation exposure in the US. Note: average – in reality the background levels go all over the place.

      The person is measuring “dangerous radiation” relative to a low radiation space to make it seem like these lenses are dangerous and should be stored away from people, but go pick up a granite rock from outside and compare it to the lenses, and the results would look similar. Why not – granite typically contains bits of thorium, uranium, even traces of plutonium.

      1. i think in this respect you are wrong. if you look at the data closely the 6.24 mSv/a is an average for the US population from ALL source which include xrays and ct which are not background radiation at all. so most likely average background radiation is much lower than that.

    4. “the normal background radiation level is about 700 microsieverts per hour”

      Oh my. That level would be lethal within about 6 months! Where do you live? It’s about 2 milisieverts per year in the bit of the UK I call home. Much higher in areas with granite.

      My own readings gave ~2.6 microsieverts per hour point blank measuring the gamma from a Thorium lens. Background from the same device lurks between 0.15 and 0.25 microsieverts, which is a wee bit more survivable. Pretty similar results considering my rather naff Giger counter can’t see Alpha or Beta.

      Didn’t buy the lens for it’s radioactive fun – more the retro lens flare and manual focus foolishness on a modern mirrorless camera. There’s almost no lens flare on the modern high end canon lenses – where’s the fun in that!

      Anyhow, if it really is 700 microsieverts per hour where you are, suggest a holiday and iodine tablets :)

  2. ” the normal background radiation level is about 700 microsieverts per hour”

    Definitely not! Correct the units, you are using.
    Even in former uranium mining sites near Příbram, Czechia, current radiation background is not higher then 1-3 microSieverts per hour:
    https://map.safecast.org/?y=49.6858&x=14.05739&z=16&l=0&m=2

    The areas near Fukushima NPP had highest dose rate about 100 microSv/h and probably highest value measured by “common” citizen (e.g. we do not talk about restricted areas close to reactors etc.) is something like 1200 microSv/h in former hospital in Pripyat, close to Chernobyl NPP.

    “Normal” radiation background is something like 0.08 – 0.30 microSv/h. Maybe you wanted to say “700 nanoSieverts per hour” but even that is still not normal background.

    1. .I have a friend who deals in antique photography and had one of these lenses in his carry on bag. TSA pulled him aside and confronted him about the radioactive device. He explained about the glass. They were not buying it. He showed them you could see right through it. They were still suspicious. Finally they let him pass though he may now be on a list somewhere

      1. Yeah, traveling with such lens is something I would never try – especially if it “gives” several dozen microSv per hour in contact – I know people got caught even with more common things like small bag of sand (there is the black thorium sand in India and Brazil – just fill a bag on the beach).

        At least the currently manufactured uranium glass should be safe to bring onboard:
        https://flic.kr/p/2ioNTiz

        But there are common issues with old military dials (airplane altimeters etc,), vintage alarm clocks etc. using radium colors for the glow-in-the-dark parts.

        1. I’ve brought some fairly hot uranium glass home in carry-on luggage (no matter where I go, I seem to find antique stores and used book stores) and never had problems. (carry-on because I’d like to get my glass home in one piece, y’know?)

    1. I think it’s been picked up on :)

      Varies quite a lot. General rule of thumb, igneous rocks are higher dose while sedimentary rocks are lower. So if you’ve got hard water furring up your kettle, good chance your background dose is on the lower end of the spectrum. Win some/loose some :)

      Don’t think it’s a safety concern not getting the number right though, as it won’t suddenly facilitate people to wind up their daily dose. That being said, there are 6 radioactive sources in my study – all very low level and quite well characterised and I’d argue safe (sealed and safe for use as teaching aids). As suggested in the article, the Thoriated glass camera lens which puts out gamma (albeit not much), sits a few m away from the desk. Except now of course, it’s next to the mouse with a Giger on top of it happily clicking away.

      The main radiation hazard for makers is likely presented by tinkering with high voltage and vacuum – then inadvertently creating an x-ray generator. Very easy to generate a lot of dose in one of those.

  3. The lenses shown are quite impressive: f/1.2, 57 mm and 58 mm. I own a couple of the Canon lenses in the middle; they have the annoying property of some internal part loosening so that the lens no longer stops down.

  4. 1. Google Oklo. Yes plutonium is a “naturally” occurring element, albeit rare.
    2. If you are really concerned about thorium, get rid of your Coleman gas lanterns. The mantels are made from thorium.

  5. Thorium in glass makes Alpha particles.
    OK.
    How far do Alpha particles penetrate through glass?
    Far less than a micron!
    The only radiation exposure is going to be from Thorium atoms within 1/20th micron of the surface of the glass.
    The total amount of Thorium atoms where they can emit Alpha particles from the glass is minute!
    Concerns about radiation exposure from glass dust?
    The bigger hazard would be the kilograms of dust in your lungs it would take for a dangerous Alpha exposure.
    A single sheet of paper can stop any Alpha…

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