It wasn’t so long ago when Canon issued a warning to users of the EOS 650D D-SLR that the front rubber grip on some cameras may turn white and cause an allergic reaction on skin.
This of course, was for a production lot that was manufactured between May 31st and June 15th, 2012. Canon determined after enquiry that the rubber grip contained a substance called zinc bis that made the surface of the grip turn white. High temperature and high humidity were the factors contributing to this condition. In rare cases, this caused skin irritation. Websites are also rife with talk that camera lenses could be radioactive. The main source of radioactivity in lenses lies with the type of glass used in them. Upto 30% of the weight of glass used in lens elements consists of thorium oxide. Thorium oxide has been replaced by calcium fluoride or fluorite by some manufacturers. Lenses containing thorium can cause moderate to severe browning of the lens elements.
Radiation levels are important only if they are above a certain level. After all, remember that in your day to day life, you are exposed to radiation when you take a plane journey or when you take an X-Ray. The tip is to keep the device emitting radiation as far away from the human body as possible. This would imply that eye-pieces made from thorium should be kept away as far as possible. Also, the heavier the lens and the glass elements, the higher the thorium content and therefore the radiation. Smaller lenses are therefore safer.
Before all of you panic and keep your lenses away, the good news is that thorium is no longer used in modern lenses. Camera makers have moved to fluorite. However, lenses produced until the 1970s did have thorium content. It is believed that Kodak was the biggest producer of radioactive lenses with its Ektar and Ektanon series. However, lenses made by Canon, Olympus, Fuji, Carl Zeiss and Pentax in the 50s and 60s have also tested radioactive.
So not very good news for storers of old, classic lenses!
H. S. Billimoria