Focusing motor generally refers to the ultrasonic motor focusing system

      Making the focusing process fast and accurate has always been the research goal of various camera and lens manufacturers. Generally, the autofocus system is driven by a traditional electromagnetic motor. Most manufacturers design autofocus systems that drive the lens with the body motor. Canon's EF lens has a built-in AF motor in each lens, and the AF speed is slightly affected by the body level.

      Generally, focusing motors can be divided into two types: ring and micro. The former is mostly used on large aperture and super telephoto lenses, while the latter is mostly used on small and cheap lenses. The difference is that the ring type ultrasonic motor can achieve full-time manual focus, but the micro no. In 2002, Canon introduced the smaller Micro USM II micro-ultrasonic motor, which made the size of the lens smaller.

      The structure of this type of motor is very simple, mainly composed of a bottom ring stator (Stator) and a ring rotor (Rotor), which converts the vibration of ultrasonic frequency into rotational energy. Applying alternating current to the piezoelectric ceramic part at the bottom of the stator will cause the stator to generate a high-frequency and fine vibration of 0.001mm amplitude and about 30kHz, so that a flexural traveling wave will be generated on the part of the top of the stator in contact with the rotor. wave). The frictional force generated by the bending moving wave is sufficient to rotate the rotor.