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SezzySue's picture
Submitted By: SezzySue
Joined: Jan 4 2006
Posts:
What is USM
Posted: January 14, 2006 - 10:29am

I know what the IS stands for and what it does, but what is the USM mean and do?

17-85mm IS/USM

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David B. Brooks's picture
Submitted By: David B. Brooks
Joined: Apr 19 2011
Posts:
#1
Re: What is USM
Posted: January 14, 2006 - 12:54pm

The USM designation refers to Canon UltraSonic motor that drives the focus movement with auto-focus operation. It I think was so named in part because the USM lenses auto-focus silently, but the more important value is the USM motor is very much faster and more exact than the older geared servo drives used in auto-focus lenses.

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