The trial production of this lens started in 1941. Canon Inc. started as “Seiki Kogaku (Precision mechanics and optics)”. This was the first interchangeable lens for Seiki Kogaku and it was advertised in the May 1947 issue of the monthly magazine “Kouga”. The focus control system is not coupled to the rangefinder and focus is decided by guess. The original standard bayonet mount was changed to the S mount, before it was marketed as the first interchangeable lens for Seiki Kogaku. This series of lenses were named “Serenar” by a Canon employee in an in-house naming contest. The word “Serenar” was coined from “Serene”, the name of the sea on the moon (the Sea of Serenity) and an adjective meaning of “tranquil”.