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DPChallenge Forums >> General Discussion >> Canon Lense Terminology
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Canon EOS R5
Canon RF 100-500mm f/4.5-7.1 L IS USM
 10/29/2004 07:22:39 PM · #1
Can anyone tell me what the Canon Lens terminology means? AF vs EF vs USM? I assume AF is autofocus and the USM is ultrasonic motor, but what are the differences and which is best?
Canon EOS-10D
Canon EF 17-40mm f/4.0 L USM
 10/29/2004 07:42:41 PM · #2
EF is the lens mount. Electronic USM is the type of motor which drives the autofocus, as opposed to a non-USM motor which doesn't have full time manual focus.

Most things are explained in this document:

Canon EF Lens Chart (PDF)

Originally posted by rodneyg:
Can anyone tell me what the Canon Lens terminology means? AF vs EF vs USM? I assume AF is autofocus and the USM is ultrasonic motor, but what are the differences and which is best?

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