Super Takumar Lens3/23/2021
If you test 3 copies find them all radioactive, its sensible to conclude the lens is 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 use lenses of lower curvature, which are less expensive to produce. Despite statements to the contrary, lenses containing lanthanum are not appreciably radioactive - lanthanum is only 110,000th 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 elements. Other common misconceptions hold that it is the coatings of these lenses which are radioactive and brown over time, and that the browning occurs in the balsam between cemented elements. It is the glass itself that contains the radioactive ThO2, and the browning therein is caused by the radiation-induced formation of color centers in the glass matrix. Super Takumar Lens Full Set OfFor 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. A study carried out by the Physics department of Swedens Royal Institute of Technology estimates that total exposure to a professional photographer using a typical thoriated lens would amount to only 0.2 yearly allowable exposure to the eye and 0.17 to the whole body under the conservative standards of the Swedish Radiation Protection Authority. However, thoriated glass eyepieces are significantly more dangerous. They can give a very large alpha and beta particle dose to the cornea of the eye, potentially causing cataracts and other problems. Normally these particles are stopped by skin, but the surface of the eye can be quickly damaged by them, and at close range, the dose can be very high. From the 1940s through the 1960s, substantial numbers of amateur cameras were produced and sold with thoriated (containing thorium oxide) lenses, including some of the Pony, Signet, and high end Instamatic (e.g. Perhaps the most famous radioactive lenses of all were the Kodak Aero-Ektars. Curiously, in his notable 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. Sometimes this incidental radioactivity causes a significant browning of these lens elements. Some users of such lenses reported in camera blogs that they reduced the browning by exposing these lenses to the ultraviolet rays of the sun. It might be that my sample was activated during usage in the X-Ray machine. Please provide evidence of the contrary or remove this lens from list of radioactive ones. Reading somewhere that a lens may contain elements that could be radioactive is not enough to include it in the list. The radiactive elements are those at the back, not at the front. The good news is that all radiation from the rear is effectively stopped by a digital camera back (e.g. Sony Alpha 7RII). This is unfortunately not the case for the much more radioactive 7-element lenses. Yours may test positive for other types of radiation, but that doesnt mean that they all do Nonsense.
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