The history of fluorite lenses

The technology for producing synthetic fluorite crystals using natural crystals as a raw material was invented in 1950. This paved the way for it to be used as an optical material. However, producing a single crystal from fluoride requires heating materials in a vacuum for a prolonged period at over 1000℃, so there were many issues, such as equipment and manufacturing processes, that needed to be resolved before it would be possible to mass produce large quantities of large crystals with high purity.
In 1968, Canon Optron became the first in the world to successfully mass manufacture synthetic fluorite. The following year, Canon released the FL-F300mm F5.6, its first interchangeable lens to use synthetic fluorite.

(FL-F300mm F5.6: Manufactured by Canon）

The hardness of minerals can be expressed using the Mohs scale. This is a set of ten reference materials whose hardness is expressed on a scale of 1 to 10. Fluorite is a 4 on this scale, which means it is a relatively soft mineral. In other words, it is easily scratched and damaged when processed and ground into lenses, which makes the entire process technically difficult.

Canon Optron has established sophisticated grinding, polishing, and processing technologies that allow it to cover all steps of the production process from crystallization to grinding and evaporation (vapor deposition).

Mohs scale of hardness