STM - RF Lens World - Canon India

STM

Canon first introduced the Stepping Motor (STM) in the EF40mm f/2.8 STM lens. The STM has a smaller actuator than conventional ultrasonic motors (USM). This was a key factor in the development of Canon’s first pancake-type EF lens. The simple mechanical structure of the STM delivers high responsiveness and controllability when starting and stopping. There are two types of STM: a leadscrew type STM that offers exceptionally smooth AF drive, and a gear type STM that minimizes size. The gear-type STM was used in the EF40mm f/2.8 STM lens, and is currently used in a variety of RF-mount lenses. However, the RF10-20mm f/4 L IS STM was the first L lens to adopt STM, and for good reason.

The USM has an advantage for lenses with long drive stroke, but the RF10-20mm f/4 L IS STM was designed for a shorter stroke. Therefore, developers determined that an STM could be used, and still achieve good performance. The smaller actuator (compared to the USM) provides more freedom in designing the layout of the IS lens group. It is possible to place the image stabilizer (IS) mechanism on the sensor side, thus reducing peripheral blurring. Furthermore, the RF10-20mm f/4 L IS STM is the first RF lens featuring an STM that comes with a position sensor. By shortening the start-up time, the overall performance of the lens is comparable to that of the USM.