Ultrasonic motor drive
Ultrasonic motor (USM) lenses first appeared with the introduction of the EF 300 mm f/2.8L USM lens in 1987. Canon is the first camera maker to successfully commercialise the USM technology. EF lenses equipped with USM drives have fast, silent and precise autofocus operations, and consume less power compared to other AF drive motors.
There are two types of USMs, the ring-type USM and the micro USM. Ring-type USM is always preferred because of its superior performance and efficiency, and it allows for full-time manual focus operations without switching out of AF mode. Micro USM is used in cheaper lenses to bring down the overall cost of the lens. It is possible to implement full-time manual focus even with micro USM; however, this is a somewhat inelegant solution, as it requires additional mechanical components, and so has not been widely implemented.
Some USM lenses are identified with a gold or silver ring and/or the label "Ultrasonic" on the lens barrel, and some of the "L" Luxury lens line-up from Canon identify each lens as using Ultrasonic with a red emblem to match the signature red stripe.
Odpowiedz z cytatem