This extremely quiet motor is ideal for photography of events, weddings, theatre or musical performances, as well as crucial moments on the golf course – any situation where autofocus noise is obtrusive. Major improvements in autofocus response and tracking ability over standard DC motors make for instantaneous focusing and spontaneous shooting of rapidly moving subjects.
Tamron’s USD works with the high-frequency ultrasonic vibrations that are produced by a ring called a ‘stator’. Energy from the vibrations is used to rotate an attached metallic ring known as the ‘rotor’. Piezoelectric ceramic is a material that produces ultrasonic vibrations when voltage of a specific frequency is applied is arranged in a ring formation on the stator. This electrode configuration of piezoelectric ceramic causes two ultrasonic vibrations to occur in the stator. By effectively combining these two ultrasonic vibrations, it is possible to convert the energy from the vibrations that produce simple motion into energy known as ‘deflective travelling waves’, which move around the circumference of the ring. The friction between these deflective travelling waves created on the metallic surface of the stator and the surface of the rotor produces force, causing the rotor to rotate. Attached to the rotor is the focusing lens, which is given a fast, smooth autofocus movement.