 BetterPhoto Member |
Canon EF vs Canon EF USM lens I am a first time buyer of an SLR camera. What is the difference between a Canon EF lens and a Canon EF USM lens.
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Jon Close |
EF specifies the electronic mount for all EOS camera lenses. USM means Ultra Sonic Motor, and designates the type of motor that actuates the autofocus. Standard focus motors are noisy arc form drive and micro motors. USM motors are fast and silent. There are two types of USM used in Canon lenses. Micro-USM motors drive reduction gears to move the focus elements in the lens. The AF/M switch must be used when swithing to manual focus. The top of the line ring-USM motors move the focus elements directly without gearing. Ring-USM allows full time manual focus without using the AF/M switch. Canon lenses with a silver colored "Ultra Sonic" band around the barrel use micro-USM, while ring-USM lenses have a gold or red colored band.
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