A 35mm camera lens.
Camera equipment can often confuse the less-experienced photographer with complex specifications and lens types. USM is one such acronym that can be found on newer lenses. It refers to Canon's implementation of a specific improvement in lens technology. Understanding the benefits can help make crucial lens decisions a bit easier.
Definition
USM stands for "Ultra Sonic Motor" and is the name given to a type of motor found in some Canon 35mm lenses. USM is used only with respect to the Canon brand. There are more than 40 lenses that feature the USM mark.
Benefits
The built-in motor of a USM lens provides the photographer with a more precise and quicker auto-focus than regular lenses. Another benefit to their use is that they are a lot quieter than standard lenses, often favored by nature photographers who require quiet equipment for shooting wildlife and quick auto-focus for sudden action.
Disadvantages
Because USM lenses contain a motor within their construction, they are often heavier than non-USM lenses. The difference in weight might not be so noticeable on the camera, but could be of concern when carrying multiple lenses. These lenses are also more expensive than equivalent standard lenses.
Types
As of May 2010, Canon produces two types of lenses labeled with the USM mark. The Ring Ultra Sonic Motor is the best performing and more expensive option often found in many of Canon's prestigious "L" lenses. A Micromotor Ultrasonic drive is a cheaper derivative found in less expensive lenses and provides quieter operation, but lacks the precision of a true Ring USM.
Other Brands
Canon's USM is the company's own name for the ultrasonic technology that drives modern auto-focus systems. Other manufacturers have similar technologies, including Nikon's Silent Wave Motor (SWM), Sony's Super Sonic wave Motor (SSM) and Olympus' Supersonic Wave Drive (SWD). All these technolgies offer similar benefits as Canon's Ultra Sonic Motor system.
Tags: Sonic Motor, Ultra Sonic, Ultra Sonic Motor, more expensive, photographer with