Canon

75-300mm USM f4.0 UltraSonic

Various Lens Actuators

Ultrasonic Motors (USM)

In order to achieve critical autofocus, the elements within a camera lens have to move quickly, quietly, and precisely. With this in mind, Canon developed the world's first lens-based motor. Based on a totally new technology, the motor spins by ultrasonic oscillation energy. The USM is quiet and quick. Instead of a large, noisy drive-train system, electronic vibrations created by piezoelectric ceramic elements power the mechanical action of the lens, providing constant torque, with virtually instantaneous stops and starts.

USM lenses are both faster and quieter than conventional motor driven autofocus systems, and draw minimal power from the camera, draining far less critical battery power. The direct-drive construction is very simple, with no gear train. This makes it durable and efficient.

Canon makes two types of Ultrasonic lenses. Ring-type USM-equipped lenses, found in large aperture and super telephoto designs, allow manual focusing without switching out of the auto mode. Micro USM designs bring the performance benefits of Canon's USM technology to a wide assortment of affordable EF lenses. Using the optimum type of USM in the lens results in maximum efficiency and effectiveness