EF — Stands for Electro-Focus and signifies that the lens has an electronic lens mount. Since 1987 Canon SLR cameras have been designed to connect to the lens electronically. Prior to this, connection between camera body and lens was mechanical and lenses with the mechanical lens mount carried the letters FD.
EF-S — EF lenses designed to fit Canon's range of digital SLR cameras that have the smaller APS-C sensors, as in the Canon Digital...
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