see also:

• camera lenses

• lenses may be radioactive if:
  • imperfect refinement of monazite sands used to make them (c1941-55 lenses)
  • use of impure cerium (1950's - 1960's) to bleach iron salts in the glass as (colourless) ferrates are stable in glass solution
  • use of radioactive thorium (1950's to 1980's) or impure lanthanum rare earth glass element to increase refractivity while maintaining a low dispersion.
    • Kodak issued patent in 1949 for a special glass with 12% thorium and 12% lanthanum
    • later “special” lenses used up to 28% thorium oxide
  • lenses exposed to excessive radiation (but these would be rare eg. from Chernobyl region)
• the level of radiation emitted is low enough (usually ~1mrem/hr or ~5x background radiation measured close to the lens) not to be considered a health danger - but no radioactivity is good because it is additive, so one perhaps would not want carry it in your pocket every day, nor use one as an eyepiece for long periods.
• thorium 232 emits alpha particles but as it decays, the daughter products which are produced emit both alpha and beta particles and the radioactivity actually INCREASES with time as more daughter products form within the glass.
• alpha particles are not a problems as even a few centimeters of air, or a plastic lens cap will stop them, although it would be wise not to spend hours with one up to to your eye such as when used as a telescope eyepiece as they then can cause issues with your cornea.
• beta particles can pass several feet of air and can be an issue by causing fogging to photographic film or paper.
• the radioactive element makes the glue between the nearby lens elements (usually the rear ones) go yellow over decades and this causes 2 issues - it decreases light transmission (up to 1.5 stops has been noted), and it affects colour film photography (of course, with digital cameras, the auto white balance should take care of this).
• the yellowing can be remedied by exposure to strong UV light
  • wrap the filter end with aluminium foil to increase the UV dose, and expose the rear end to a UV light source 24hrs/day for 7 days - see this YouTube demo
  • some place the lens on a window sill for several months but this exposes it to dust, etc.
  • Do NOT resort to this repair method outlined on this website!
• NB. not all yellowed lenses are radioactive, the yellowing may just be due to aging of the Canada balsam used as cement.

• there are many lenses with some degree of radioactivity, but the following are more recognised:
• APO-Lanthar lenses by Voigtlander
• Rodenstock Weitwinkel Perigon (1958 vintage, 130 mm/F12)
• Kodak Aero Ektars (6“, 12”, and 24“)
• Canon Pellix 50mm lens
• Canon FL 58mm f1.2
• Canon FD 55mm f/1.2
• Micro-Nikkor 200mm f/4
• Nikkor 35mm f/1.4 (early variant with thorium glass elements)
• Leica 35mm f/2 summicron
• most Asahi Super Takumar 50mm f/1.4 lenses and SMC versions (but excluding the scarce original 8 element version)
• Super Takumar 35mm f2.0, 50mm f1.5, 55mm f2 (Asahi Optical Co.)
• Super Takumar 6×7 105mm f2.4 (Asahi Optical Co.)
• SMC Takumar 55mm f/1.8
• Super-multi-coated Macro-Takumar (Asahi Optical Co.)
• Yasinon-DS 50mm f1.7 (Yashica)
• Olympus OM 55mm f/1.2
• Olympus OM 50mm f/1.4 G.Zuiko single coated silver nosed version
• Minolta MC W. Rokkor-SI 1:2.5 28mm (early variant, before radioactive glass impurity could be banned)
• Minolta MC Rokkor-PG 1:1.2 58mm (early variant, before radioactive glass impurity could be banned)