Here’s a piece of photography history I always like to talk about: I own a Pentax 67 medium format film camera and one of the best lenses ever made for it is the SMC Takumar 50mm f1.4. This lens is (in)famous due to its amazing depth of field, image clarity, and it being a radioactive thorium glass lens! Pentax and other manufacturers in the 1960’s used thorium oxide in glass optics to improve image/optical quality (which it does).The amount of radiation emitted (beta and gamma rays) varies but averages about 7.7 uSv/hr, or about 1.41 dental x-ray’s worth of radiation, which average about 5.5 uSv/hr. Here is an excellent video that explains more about these interesting thorium glass lenses.
Jan 21, 2025

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