A lot of readers wrote in recently questioning the radioactive necessity of photographer Kelly Grider's WWII-era aerial spy lenses. I, in turn, wrote Kelly for clarification. To refresh your memory, compare results from the non-radioactive Soviet OF-233M spy lens above and the thorium-infused Kodak Aero Ektar 2.5/306mm lens below:
I, for one, appreciated starring straight into my brilliant blue iridescent reflection (courtesy of the non-radioactive Soviet OF-233M) but prefer the resulting soft, romantic edges of the Kodak Aero-Ektar. A little bit of thorium goes a long way-- sure beats wrinkle cream.
Kelly responded with this explanation:
"By design, the Aero-Ektars incorporate glass lens elements that contain significant amounts of Thorium. That the cause of the radioactivity is Thorium is indisputable, both on the basis of the documents from the the World War II era and from gamma-ray spectral measurements that I have made. The Thorium-containing glasses were used because these glasses have a high refractive index with a low dispersion (variation of index with wavelength), a highly desirable combination."
For reference, each lens is about the size of your hand and fits on the front end of Kelly's hand-built, home-made camera:
The radioactive Kodak Aero Ektar above, the non-radioactive Soviet OF-233M lens below:
Kelly's home-made camera (reference body unknown).