Canon has two different types of lens mounts. The Canon EF and EF-S lenses make up all of Canon’s SLR lenses. While they have many similarities, the differences between the two are important to understand when purchasing a lens for your new Canon SLR camera body. It all depends on the type of Canon camera body that you have. EF lenses will work with all types of Canon camera bodies but EF-S lenses will only work with certain Canon camera bodies.
Canon EF and EF-S lenses refer to the type of camera the lenses can be mounted to. In 1987, Canon made all its camera mounts universal for all its SLR cameras, both film and digital. EF stands for “electrofocus.” They are distinguished by the red dot that helps to align the lens with the camera mount when placing the lens on the camera. EF and EF-S lenses are a bayonet style mount that has electrical contacts that help the lens talk to the camera.