Stan,
You raised an interesting question.
The thought of the ultrasound being heard by some animals/birds had
crossed my mind before. I had not got to read about that actual design of
the motor until your post nudged me.
Prior to that I was somewhat dismissing "ultrasonic" assuming it could've
been just a marketing term that has nothing to do with the original
meaning of the word (as "Nano" i-Pod :-) ). But no, it looks like the
motor indeed may be using vibration at ultrasonic frequencies (above 20
kHz). I'd be curious to know which frequencies they actually use.
I have never been exposed to any work with ultrasound (short of ultrasonic
cleaners and patient side of ultrasound imaging). From the general
principles, I'd say it should be easy to damp those vibrations to avoid
"leakage" to the outside, but I don't know if anybody cared about that.
In principle, the body of the lens should attenuate the ultrasound
drastically. But only a careful measurement could tell for sure.
Or you can watch how a bat reacts when you activate AF in your SDM lens.
:-)
I'll try to do that next time I am at a zoo with bats (although they are
usually behind the glass, so it is not a "clean" experiment).
Got a barn with bats? ;-)
Or, if you have a friend who is an ultrasound imaging technician, bring
your camera with the lens, and activate AF near the imaging "probe".
If you see some distortions of the image (AF on vs. AF off), you have
leakage. If you don't, - it's inconclusive: it might be that the
frequency ranges are too different, and the imaging instrument is not
sensitive to the SDM's frequency.
Cheers,
Igor
Stanley Halpin Thu, 28 Jul 2016 06:06:36 -0700 wrote:
I went to Wikipedia to see if they could tell me what an ultrasonic motor
is, how it works, and whether it can be heard.
That last point was my first question actually. Seeing the term
“ultrasonic” triggered the thought that the sonic may be “ultra” with
respect to human hearing, but maybe birds and other animals can hear and
be alerted by the ultrasound? I suspect probably not, but Wikipedia did
not address this.
The Wikipedia article is written for someone with a technical background
and I found it unintelligible. However, they do include a list of common
application of this technology, autofocus lenses, pioneered by Canon. With
several other companies now using the technology under various names
including Sigma HSM, Tamron USD, PZD, Nikon SWM, Olympus SWD, and Pentax
SDM.
stan
--
PDML Pentax-Discuss Mail List
PDML@pdml.net
http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow
the directions.
