Camerapedia has listed 54 lenses that are tested to be radioactive.
There are a significant number of lenses produced from the 1940s through the 1970s that are measurably radioactive. Main source of radioactivity is the use of thorium oxide (up to 30% by weight) as a component of the glass used in the lens elements. Thorium oxide has a crystalline structural similar to calcium fluoride (fluorite). Like fluorite, its optical properties of high refractivity and low dispersion allows lens designers to minimize chromatic aberration and utilize lenses of lower curvature, which are less expensive to produce. Contrary to often seen statements to the otherwise, lenses containing lanthanum are not appreciably radioactive – lanthanum is only 1/10,000th as radioactive as thorium. Radioactivity in lanthanum containing lenses is due to the intentional inclusion of thorium in the optical glass mix. The presence of thorium can sometimes, depending on the mixture of other elements in the lens, cause moderate to severe browning of the lens element(s).
Typical radiation levels can approach 10 mR/hr as measured at the lens element’s surface, decreasing substantially with distance; at a distance of 3 ft. (.9 m.) the radiation level is difficult to detect over typical background levels. For reference, a typical chest x-ray consists of about about 10 mR, a round-trip cross country airline flight exposes a passenger to 5 mR, and a full set of dental x-rays exposes the patient to 10 mR to 40mR.
Most smaller lenses with thorium elements are not very dangerous. However, thorium eyepieces are dangerous. They can give a very large alpha and beta particle dose to the cornea of the eye, causing cataracts and other problems. Normally these particles are stopped by skin, but the surface of the eye is quickly damaged by them, and at close range, the dose can be very high. – “source camerapedia’
Head over to Camerapedia to check if you own any of these lenses.
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