The short answer is to read this:
http://en.wikipedia.org/wiki/Ultrasonic_motor
My understanding is that USM, HSM, SDM, etc, &s shouldn't be likened
to conventional electric motors with their armatures and brushes and
all the other stuff (I'm sure that's a technical term, I've heard an
engineer use it). In the most elegant examples the USM is an annular
linear motor that encircles the component to be shifted, be that the
focusing helix or the diaphram mechanism. In that application RPM
doesn't apply, because the total range of movement is less than 360
degrees. A straight linear motor applying its movement in one
location could possibly shift the focusing group directly without a
helix, but I'm unsure if any USM systems are powerful enough to
directly move the lens without a helix or gear train to step up the
torque, and I couldn't be arsed to research it myself. And some USM
motors resemble a can motor (one configuration of a standard electric
motor) with an output shaft, but differ in that they excite the
rotation by a different method which has less mechanical resistance
and thus spins more freely.
IIRC the first linear drive lenses were in the Rolleiflex SLX 6x6
system, but don't know if USM was used. The technology ~was~
available at the time.
regards, Anthony
"Of what use is lens and light
to those who lack in mind and sight"
(Anon)
On 5 February 2010 10:27, Larry Colen <l...@red4est.com> wrote:
> Do the motors turn at 900,000 RPM (15,000 hz * 60)?
>
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> Larry Colen l...@red4est.com sent from i4est
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