Many lenses produced from the 1940s through the 1980s are measurably radioactive. The 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.
Many lenses produced from the 1940s through the 1980s are measurably radioactive. The 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.
In 1945, Eastman Kodak Company, filed a patent for Glass formulation[1], which introduced thorium and lanthanum oxides in boric optical glass for optical properties. This application relates to glass having optical values in a range that is useful for the designing of optical instruments. Specifically, this application relates to such glass having an index of refraction for the D line (n) in the range between 1.65 and 1.68 and an Abbe value (v) between 52.5 and 57.0.
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), which can be reversed by the action of photons (bright light) and UV light.[2]
By far the most prolific producer of radioactive lenses was Eastman Kodak. From the 1940s through the 1960s, substantial numbers of amateur cameras were produced and sold with « thoriated » lenses (containing thorium oxide), including some of the Pony, Signet, and high end Instamatic cameras. In addition, many professional level Ektar lenses from this era contain thorium. Perhaps the most famous radioactive lenses of all were the Kodak Aero-Ektars.
Curiously, in his book, A History of the Photographic Lens, Rudolf Kingslake (head of the Eastman Kodak lens design department 1937-1968), makes only a single passing comment on the possible use of thorium in Kodak lenses.
Kodak lenses tested radioactive (by John Hufnagel)
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- Kodak Ektar 101mm f/4.5 (Miniature Crown Graphic camera) lens mfg. 1946
- Kodak Ektar 38mm f/2.8 (Kodak Instamatic 814 camera) lens mfg 1968-1970
- Kodak Ektanar 50mm f/2.8 (Kodak Signet 80 camera) lens mfg. 1958-1962 (3 examples)
- Kodak Ektanar 90mm f/4 (Kodak Signet 80 camera) lens mfg. 1958-1962
- Kodak Ektanar, 44mm f/2.8 (Kodak Signet 30, Kodak Signet 50, Kodak Automatic 35/Motormatic 35 cameras) lenses mfg. 1959-1969
- Kodak Ektanon 50mm f/3.9 (Kodak Bantam RF camera) lens mfg. 1954-1957
- Kodak Ektanon 46mm f/3.5 (Kodak Signet 40 camera) lens mfg. 1956-1959
- Kodak Anastar 44mm f/3.5 (Kodak Pony IV camera)
- Kodak Color Printing Ektar 96mm f/4.5 lens mfg. 1963
Kodak lenses reported elsewhere as radioactive
- Kodak Aero-Ektars (various models)
- Kodak Ektanon 50mm f/3.9 (Kodak Bantam RF camera)
Non-Kodak lenses reported as radioactive
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- Canon FD 17mm f/4.0 SSC
- Canon FL 50mm f/1.8
- Canon FD 55mm f/1.2
- Canon FL 58mm f/1.2
- Canon FD 35mm f/2.0 (versions from the early 1970’s)
- Carl Zeiss Jenna Flektogon 35mm f/2.8
- Ernst Leitz GmbH Wetzlar Summicron f=5cm 1:2 (collapsible, M39)
- Fuji Fujinon 50mm f/1.4
- GAF Anscomatic 38mm f/2.8 (GAF Anscomatic 726 camera)
- Konica Hexanon AR 57mm f/1.2
- Mamiya Sekkor 55 f/1.4
- Nikkor 35mm f/1.4 (early variant with thorium glass elements)
- Olympus G.Zuiko AUTO-S 50mm f/1.4
- Super and Super-Multi-Coated Takumar 50mm f/1.4 (Asahi Optical Co.) [5]
- Super- and Super-Multi-Coated Takumar 20mm f/4.5, 35mm f/2, 55mm f/1.8, 55mm f/2 and 85mm f/1.8 (Asahi Optical Co.)[5]
- Super Takumar 6×7 105mm f2.4 (Asahi Optical Co.) [6]
- Tōkyō Kōgaku UV-Topcor 50mm f/2
- Tōkyō Kōgaku GN-Topcor 50mm f/1.4
- Voigtlander Zoomar 36-82 f/2.8
- Yashica Yashinon-DS 50mm f/1.7
- Yashica Auto-Yashinon-DX 50mm f/1.4
Sometimes the radioactive glass elements show a significant yellowing, which not only changes the color of the picture but can cost 1/2 to 1 stop of light. Early research by the US military showed that glass exposed to radiation can be discolored in this way, and that exposure to bright light (fotons) will bring the glass back to its natural clear state. [2] Over the years, the users of discolored lenses have reported that exposure to sunlight, UV lamps, or bright LED lamps healed the yellowing. The sunlight procedure is carried out by placing the lens on a window sill and needs several days of sunny weather to have a positive effect. UV and LED lights might need more or less time depending on the intensity of the light.
The healing of yellowing by sunlight is also reported for some lenses with thorium glass elements, for example for the Nikkor 35mm f/1.4 lens, Voigtlander Zoomar, and the Super Takumar 50mm f/1.4 lens.
http://camera-wiki.org/wiki/radioactive_lenses
Brevet : https://patents.google.com/patent/US2466392A/en
Déposé par PAUL F. DE PAOLIS en 1945
https://patentimages.storage.googleapis.com/85/b0/a3/091c5844d65fe0/US2466392.pdf
Les verres décrits ici sont caractérisés, outre les valeurs optiques mentionnées, par la présence en quantité substantielles, plus de dix pour cent de chaque, d’oxydes de lanthane, de tungstène et de thorium, représentant au total près de soixante pour cent de l’ensemble du lot.
J’ai constaté que les ingrédients, lorsqu’ils sont présents dans les proportions spécifiées dans les revendications, permettent d’obtenir, avec la technique verrière ordinaire, un verre présentant une transparence, une dureté, une stabilité et une résistance aux intempéries élevées et capable de supporter un polissage élevé et de supporter les procédés ordinaires de traitement du verre utilisés dans la fabrication de pièces optiques.
https://patentimages.storage.googleapis.com/5a/09/77/131256754ebada/US2434147.pdf