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09/05/2006 12:05:32 AM · #1 |
| I was looking on the canon website for lenses could somebody tell me what the difference between USM and non USM versions. |
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09/05/2006 12:07:46 AM · #2 |
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09/05/2006 12:10:09 AM · #3 |
I believe USM stands for Ultra-Sonic Motor, meaning it makes no sound. Every manufacturer has a version of this, and most new lenses have USM equivolent silent lenses.
To quote Wikipedia:
[quote]Dry friction is often used in contact, and the ultrasonic vibration induced in the stator is used both to impart motion to the rotor and to modulate the frictional forces present at the interface. The friction modulation allows bulk motion of the rotor (i.e., for farther than one vibration cycle); without this modulation, ultrasonic motors would fail to operate.
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A key observation in the study of ultrasonic motors is that the peak vibration that may be induced in structures occurs at a relatively constant vibration velocity regardless of frequency. The vibration velocity is simply the time derivative of the vibration displacement in a structure, and is not (directly) related to the speed of the wave propagation within a structure. Many engineering materials suitable for vibration permit a peak vibration velocity of around 1 m/s. At low frequencies --- 50 Hz, say --- a vibration velocity of 1 m/s in a woofer would give displacements of about 10 mm, which is visible to the eye. As the frequency is increased, the displacement decreases, and the acceleration increases. As the vibration becomes inaudible at 20 kHz or so, the vibration displacements are in the tens of micrometers, and motors have been built [Shigematsu, et al., IEEE TUFFC 2003 50(4), pp 376-85] that operate using 50 MHz [[surface acoustic wave (SAW)]] that have vibrations of only a few nanometers in magnitude."[/quote]
As you can see, the use of designated vibration velocity is key when it comes to audible sound waves and vibration.
:-P
No, I don't really mean to imply I have any clue as to how it works. But that's what it stands for. Ultra-Sonic Motor. |
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09/05/2006 12:12:50 AM · #4 |
Simply stated anything ultra-sonic produces soundwaves out of our sensory range, which makes for a quiet experience for you and any person around you. It may however drive your dog nuts :-)
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09/05/2006 12:15:20 AM · #5 |
UnSharp Mask lens? hehe
maybe someday they will make USM (ultra sonic) mirror-flaps
so dSLR no longer have to scare birds away when shooting candid wildlife |
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09/05/2006 12:18:49 AM · #6 |
Originally posted by crayon:
maybe someday they will make USM (ultra sonic) mirror-flaps
so dSLR no longer have to scare birds away when shooting candid wildlife |
No way, I love the click-clack of the mirror flapping. It lets me know I'm holding a real camera.
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09/05/2006 12:20:23 AM · #7 |
| Well i was going for a lens that would be good for portrait photography. so will i need a lens with USM. |
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09/05/2006 12:24:22 AM · #8 |
Originally posted by crayon:
UnSharp Mask lens? hehe
maybe someday they will make USM (ultra sonic) mirror-flaps
so dSLR no longer have to scare birds away when shooting candid wildlife |
Electronic shutters don't have to make any noise as far as I know, so a rangefinder or point and shoot/live preview SLR with a CCD could be silent. |
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09/05/2006 12:31:23 AM · #9 |
Originally posted by kingsley:
Well i was going for a lens that would be good for portrait photography. so will i need a lens with USM. |
No, save your money and buy the best optiics you can get.
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