What is a Fluorite Lens?
Fluorite is a naturally occurring substance, which just so happens to possess near perfect light dispersion qualities. These qualities mean that they are a good choice for use in optical equipment, for where ultra high quality is a must. For this reason, fluorite has been used in optical equipment, such as microscopes, since the 1920’s.
A Little More Detail:
The only problem is that fluorite can not be harvested in sufficient quantity and quality in the natural environment. Canon’s engineers found a way around this issue, by synthetically growing fluorite crystals in a laboratories. Even then, it is still a very complex job to turn Fluorite in to a lens product. For this reason, Fluorite lens elements are only found in the very best Canon lenses
, such as the EF 100-400mm F4-5.6 L USM II