Patent ID: 8149520

Claim:
A rotary actuator comprising: a multi-polar magnet, in which north and south poles are alternately arranged in a circumferential direction, said multi-polar magnet being shaped into one of a circular ring and a circular arc member; and a coil body having coils which are provided around said multi-polar magnet to be capable of moving in said circumferential direction of said multi-polar magnet, each of said coils substantially lying on a plane that extends in a radial direction of said multi-polar magnet and that is orthogonal to said circumferential direction of said multi-polar magnet, wherein said north and south poles of said multi-polar magnet are positioned apart from each other by a first predetermined interval in said circumferential direction, said coils are positioned apart from each other by a second predetermined interval in said circumferential direction, said first predetermined interval being an integer multiple of said second predetermined interval, said rotary actuator is applied to a focusing mechanism of a photographic lens of a camera system, one of said coil body and said multi-polar magnet is fixed to said photographic lens, the other of said coil body and said multi-polar magnet is provided on a gearing ring which is geared to a focus ring of said photographic lens, such that manually rotating said focus ring causes said gearing ring to rotate, and an auto focusing operation of said photographic lens is controlled by passing currents through said coils.