November 11 2021
I was contacted by a student recently who asked “I was just told that all my old lenses are radioactive and dangerous, is that true?” He was quite concerned as he loves shooting vintage lenses but was concerned about the potential health risks. I reassured him and explained that some lenses (not all) made from 1940 thru the 1970’s do utilize radioactive thorium oxide ThO2 to reduce reflections and generally improve optical performance. However the radiation levels should not be concerning, unless you sleep with it and use the lens for hours on end every day. The radiation levels are generally quite low and almost undetectable at distances of a meter or more. Having the camera body between the lens and your face also effectively cuts the levels in half.

The lens in the photo below has a radiation level of 0.105 mR/h which is classified as a “high level”. All tests were done using a GQ GMC Geiger Counter. Measuring through the camera body resulted in a level 0.046 mR/h. Moving the counter 1 m from the lens, there was no detectable radiation above normal background levels. Putting the lens in a cabinet with glass doors, completely blocked all radiation from the lens. 

Lets put this in perspective: 

Round Trip Cross Country Airline Flight 5.0 mR/h
Hospital X-Ray 5.0 - 10.0 mR/h
Dental X-Ray 10.0 - 40.0 mR/h

Compare those with this lens at 0.105 mR/h and you can see the levels are very low. However radiation injury can be cumulative so sleeping with the lens on your night stand and carrying it on your person 16 hours a day 365 days a year, might be something I personally would reconsider. It’s also important to understand that the majority of lenses are not radioactive. I have tested about 40 lenses this week and only 5 of them are radioactive.

The biggest danger with radioactive lenses is caused when the glass becomes broken or damaged. This may result in tiny particles of glass containing thorium becoming airborne. The radiation does not penetrate clothing or skin well, but if inhaled or ingested, it can be cause for concern. Protect these lenses and if they become damaged you should contact your local authorities for advice on proper disposal. Beyond that, have fun with these beautiful old lenses. Besides, it's fun to see the reaction when you tell people your lenses are radioactive! 
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