Focusing Mechanism


STM Focusing Mechanism is it the Same as USM?

The terms STM and USM are used specifically by Canon to define the mechanism used by the lens. This in turn helps to elaborate the purpose of the lens. Different companies have different names for lenses often meant for the same purpose. For instance, Olympus uses the term MSC (Movie and Still Compatible) and SWD (Supersonic Wave Drive) for the STM and USM mechanism respectively. Nikon uses the terms SWM (Silent Wave Motor) instead of USM.

There is very little advantage of an replacing a normal motor with an ultrasonic motor in an otherwise standard lens.

STM Lenses

The term STM stands for Stepping Motor and is the latest range of lenses offered by Canon. The STM lenses are optimised for video. The mechanism in these lenses makes use of contrast-detect autofocus

When used with latest Canon cameras, these lenses provide continuous autofocus in Live View video recording, a first in DSLR cameras. However, this technology is still new and only four Canon lenses of this nature are currently available in the market.

USM Lenses

Most high-end and professional lenses incorporate this technology. USM stands for the Ultrasonic Motor that drives the lens to get the focus right. USM lenses are best when shooting still photographs. The lenses with this mechanism are fast, consume less power and optimised for phase-detect autofocus sensor making them precise for DSLRs. It consists of two metal rings which vibrate at a very high frequency making high speed focusing a possibility. It is also called as ring-type USM.

Canon has also introduced lenses with a new micro motor USM. It replaces the magnetic motor on a standard lens with a ultrasonic motor. Though cheaper, these budget lenses do not come close to the focusing speeds of a ring-type USM.