Ultrasonic motors.
Ultrasonic motors do not rely on magnetic coils like most electric motors. Instead they use extremely high-frequency vibrations which translate into circular motion.
USM
Ultrasonic Motor - This is a special type of motor within a modern autofocus lens that allows for extremely quick focus shifts with very little sound.
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Difference in Lens MM Rankings ...
USM is "ultrasonic motor". All Canon EOS-system lenses have built-in focus motors. There is no motor in the body as is the case with Nikon, for example.
Canon - Ultrasonic Motor (USM)
Nikon - Silent Wave Motor (AF-S)
Olympus - Supersonic Wave Drive (SWD)
Pentax - Supersonic Drive Motor (SDM)
Sigma - Hypersonic Motor (HSM)
Sony - Supersonic Wave Motor (SSM) ...
Canon's USM / UltraSonic Motors, are also famous for being quieter than standard motors used in cheaper lenses. This is useful for wildlife photographers, where animals and insects could become spooked from noisy camera parts.
USM - Canon's UltraSonic Motor, a fast auto focus motor used in their high quality EF lenses and in the Powershot Pro 1 fixed-lens digicam.
USM stands for Ultrasonic Motor. This abbreviation depends on the manufacturer (Nikon uses SWM, Sony uses SSM and Sigma uses SDM) but means that the lens has a motor inside that can move the lens quickly to change focus.
Ultrasonic Motors ...100
Image Stabilization ...100
Information on a Canon Lens ...101
Lens Peripheral Illumination Correction ...102
Focal Length ...103
Zoom Lenses ...104
Normal Lenses ...105
Wide-Angle Lenses ...106
Telephoto Lenses ...108 ...
And, luckily for us, there are no ultrasonic motors or focusing mechanisms to worry about, only diaphrams and (usually) shutters. This means that there is not that much that can go wrong.
These include such world’s firsts[i] as the Ultrasonic Motor-powered lens (USM), Image Stabilizer (IS) to compensate for the effects of camera shake, Subwavelength Structure Coating (SWC) anti-reflection technology, ...
Tamron 18 - 270mm f/3.5-f/6.3 DI-II VC PZD Piezo Drive Ultrasonic Motor Aspherical (IF) AF Zoom with Macro, for Nikon AF Digital SLRs with APS-C Sensors, USA
$649.00 Price is before discount
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USM (Canon): UltraSonic Motor; Canon's fastest, quietest autofocus lens mechanism
VR (Nikon lenses): Vibration Reduction ...
8 aperture throughout the zoom range, Canon’s three-stop image stabiliser — allowing you to use a shutter speed of just 1/15th of a second in low-light conditions — and a high-speed, silent ultrasonic motor autofocus mechanism, ...
Renowned for ultra fast, ultra quiet, precision autofocus. Each Canon EF lens has its own microprocessor controlled focusing motor for optimum performance. Many utilize Canon's exclusive Ultrasonic Motor technology.
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