
Originally Posted by
Bryan Carnathan
While the 135 L features a fast, accurate and silent USM (Ultrasonic
Motor), the Canon EF 135mm f/2.8 With Softfocus Lens uses older AFD
(Arc Form Drive) technology.
This AFD implementation is not loud or slow focusing for a non-USM
lens, but not as fast or quiet as the more-modern USM lenses -
and it does not provide FTM (Full Time Manual) focusing.
The 135 SF's manual focus ring is small, does not turn smoothly (the
gears engaging inside can be felt) and has play in it.
The 135 SF's MF (Manual Focus) switch feels cheap and also does not
work smoothly.
Both lenses focus internally (do not change size) and have non-rotating
front elements.
The 135 SF autofocuses even in softfocus mode.
The 135 SF lens also proved to be difficult to get accurate focus with.
While it nailed autofocus on most of my close portrait shots, other subjects proved to be difficult for it.