Rotary actuator for auto-focusing a camera lens

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.