Canon EF Lens Technology

Built-In motor and EMD

Built-In Motor and EMD

Canon EF lenses (except TS-E and MP-E lenses) have a built-in AF motor. Compared to camera body-based AF motors, lens-based motors have driving energy with lower transmission loss. The optimum AF motor for the particular lens can also be selected and installed. The AF operation is therefore quick, quiet, and highly precise. The lenses also have an EMD (Electromagnetic Diaphragm) to control the aperture electronically. The aperture can be set either with an electronic dial or with the electronic pulse signal sent according to the exposure reading. Aperture control precision is therefore unmatched.

Inner Focusing and Rear Focusing

An inner focusing lens has the focusing lens group(s) in front of the diaphragm, while a rear focusing lens has the focusing lens group(s) behind the diaphragm. Both focusing systems allow the focusing lens group to be small. This minimizes the load on the actuator which drives the autofocus. In turn, the AF speed is faster. The whole optical system can also be made more compact. Also, since the lens does not rotate during focusing, the effects of a circular polarizing filter or gelatin filter remain intact.

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