A Radioactive Lens
Between the 1940s and 1970s, a number of camera manufacturers designed lenses employing thoriated glass in one or more elements. Incorporating as much as 40% thorium dioxide (ThO2) in the glass mixture increases the index of refraction of the glass while maintaining low dispersion. Thoriated glass elements allowed lenses to deliver low levels of aberration and distortion with relatively simple and easy to manufacture designs.