Canon's Long History of Growing Fluorite Crystals for Lenses

Canon began synthesizing fluorite crystals in 1967 to address secondary chromatic aberration, a color error that worsens with focal length and is difficult to correct with ordinary glass. The first lens to incorporate these synthetic fluorite elements was the FL-F300mm f/5.6, released in 1969. Fluorite's unique dispersion properties allow for apochromatic correction, bringing three wavelengths of light to a common focus, which is crucial for sharp images in long telephoto lenses where this aberration is most pronounced.