
Camerapedia recently published a list of 54 lenses that contain some radioactivity and if you use any of them regularly, it is necessary to take note. Some old cameras manufactured between the 1940’s and 1970’s used thorium glass elements. Thorium oxide was considered as a useful material to reduce dispersion and improve refraction. This allowed manufacturers to use more affordable high-quality glass when designing a lens with less curvature.
Kodak was a prolific user of thorium glass elements during their manufacturing activities. Eleven lenses made by Kodak are mentioned in the list. Camerapedia says that these lenses may emit as much as 10 mR per hour of radioactivity, which is roughly equal with a session of chest X-ray. If users still insist to use any of these lenses, it is advisable to use them no more than one hour per day to avoid negative long-term effects.