In the late 1980s, Canon began replacing its award-winning FD Lens Series with even better glass, designated as the EF Series. This new series incorporated next-generation design specs and was developed with the entire camera line in mind. Each lens starts with an ideal, large diameter mount, which permits perfect communication between the camera and the lens’ autofocus actuators and the electromagnetically driven precision diaphragm that controls the iris. Canon’s Ultrasonic Motor (USM) was originally meant only for the L series lenses but is now found on almost all cameras in the EF Series.
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