| AL | A special lens element with a surface curved with the ideal shape to correct spherical aberrations, i.e., a lens having a free-curved surface which is not spherical, is called an aspherical lens. |
| CA | Circular Aperture. A new diaphragm unit, which uses curved aperture blades to provide for a more rounded opening as the lens is stopped down. It's especially effective at rendering out of focus background highlights as natural rounded shapes. |
| I/R | Inner/Rear focusing ring. Focusing is performed by moving one or more lens groups positioned between the front lens group and the diaphragm. |
| S-UD | Super Ultra-low Dispersion glass. Is better than UD but still worse than CaF2. |
| EF | Electro-Focus. EF-series lenses for Canon EOS series. Bayonet mount with three outer lugs. |