In order to
achieve critical autofocus, the elements within a camera lens
have to move quickly, quietly, and with exacting precision. To
accomplish this, Canon developed the world's first lens-based
Ultrasonic Motor (USM). Based on a totally new technology, the
motor spins by ultrasonic oscillation energy. In effect,
instead of a large, noisy drive-train system, electronic
vibrations created by a piezoelectric ceramic element power
the mechanical action of the lens. In a very broad comparison,
it's like the difference between a mechanical watch with gears
and springs and quartz-timed watch movement. Therefore, torque
is constant and start and stop functions virtually
instantaneous.
By making the autofocus operation almost
inaudible and by accelerating the autofocus speed, this type
of motor greatly expands the shooting possibilities for Canon
photographers. There is virtually no whining noise as the lens
focuses to distract the subject or draw attention to the
photographer. Most important for the photographer in the
field, the motor draws minimal power so the camera batteries
last longer.
You'll find two types of Canon Ultrasonic
Motors in the camera lens system, each optimized for maximum
efficiency and effectiveness. Ring-type USM-equipped lenses,
found in large aperture and super telephoto designs, allow
manual focusing without switching out of the auto mode. It's a
direct-drive system that provides all the above advantages.
Micro USM designs bring the performance benefits of Canon's
USM technology to a wide assortment of affordable EF lenses.
Extremely compact and light, this USM is even used on lenses
as small as the EF 28-90mm and EF
22-55mm. |