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Home » Glossary » USM

USM

Two definitions for this one.

Unsharp Mask

A unsharp mask is a technique used to sharpen images.  It dates back to a darkroom technique, but the name has stuck with digital photography; especially considering that almost all digital images require some type of sharpening.   

PPF has a thread with a very good explanation of how the unsharp mask, the original darkroom technique, works. 

UltraSonic Motor

This is the type of motor Canon uses in many of their EF lenses.  The advantage is that a USM motor is quieter and typically allows you to override it and focus manually. 
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