Ef 300mm – Canon EOS-1 User Manual
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--V
li 1 *
EF 300mm
//J’.Si
USM
Some L series lenses employ an
ultrasonic motor that handles AF
operation within the lens. USM
incorporates a ring-shaped motor.
As it is a direct-drive system with no
gearing units, operation is fast and
reliable. Added to the fact that there
are no mechanical couplings
between the lens and camera body,
this technologically-advanced lens
focusing system allows astonishingly
quick, precise operation. Greater
compactness and operational
simplicity are realized by using low
rotational speed and high torque.
thereby eliminating the need for
a braking unit. Beyond being quick,
focusing operation is also virtually
noiseless.