Glossary | Telescopes | Optics | Coating | FMC
FMC stands for fully multi-coated.
FMC is the usual abbreviation for the term fully multi-coated. The coating process places a special layer over the optical surface of a lens in order to reduce reflection. In the case of multi-coating, several layers are used, each optimised for a given wavelength range.
The designation "fully" means that all air/glass surfaces are multi-coated, not just the outer surfaces.