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My Canon lenses have the designation USM on them, which I assume is for the same reason that they say "Ultrasonic". What does this mean, and why or why do I not want it?

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This is probably covered at a high level by What do all those cryptic number and letter codes in a lens name mean? –  chills42 Nov 4 '11 at 15:16
I guess we should probably close this as a duplicate, since the wiki chills linked is pretty much the source for such information. Any objections? –  jrista Nov 5 '11 at 2:55
@jrista: My only argument there is that I think that the last phrase (why or why do I not want it) makes this a different (more specialized) question. –  chills42 Nov 7 '11 at 16:09
@chills42: Good point. I've left it open anyway, so I guess all is good. ;) –  jrista Nov 8 '11 at 6:40
With that in mind I suggest we mod the title to "What is USM and what are the Pro and Cons" or similar –  Gapton Nov 8 '11 at 14:52
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3 Answers

up vote 20 down vote accepted

USM - Ultrasonic motor (This is the Canon Terminology)

This is a big improvement over older micro-motor based autofocus systems, which are significantly slower and louder. There are two types of USM systems "Micro" and "Ring". The preferred type is "Ring Type" which always allows for manual focus without turning off auto-focus.

Benefits of Ultrasonic motors:

  • Faster focusing
  • Quieter
  • Full time manual focus (for ring-type USM)


  • Higher Cost


USM is a Canon trademark, so similar terms are used by other manufacturers. These other names include:

  • USM: Ultrasonic Motor (Canon)
  • SWM: Silent Wave Motor (Nikon)
  • SWD: Supersonic Wave Drive Motor (Olympus)
  • SDM: Supersonic Drive Motor (Pentax)
  • SSM: In-Lens Super-sonic Motor (Sony/Minolta)
  • HSM: Hyper-Sonic Motor (Sigma)
  • USD: Ultrasonic Silent Drive (Tamron)
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another downside: weight. Another name for USM Nikon uses is AF-S (Auto Focus - Silent wave). –  jwenting Nov 10 '11 at 10:26
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Ultrasonic Motor

You want it for a few reason:

  • nearly silent AF (important for photographers working with animals)
  • Full-time (even when AF is on) manual focus (important for macro)
  • It is much faster than non-USM focusing (especially useful for tracking moving subjects)

You may NOT want it because:

  • Lenses with USM are more expensive

Call me dumb but after few minutes of hard-thinking I still cannot come up with ANY other reason you may NOT want it. Making my answer almost identical to the previous one lol.

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As many people have mentioned USM = Ultrasonic motor. Its a small motor built into the lens. This means that the camera will focus MUCH faster without making noise (or much noise). There are actually 2 kinds of USM, "Ring Ultrasonic" (good) and "Micromotor Ultrasonic" (not so good) see here. If you're interested in a more technical explanation form canon, see here.

Amazon shows a 50mm lens at $100 for the non USM and $300 for the USM. AFAIK its the same glass in in both, so you're paying for the quick and quite motor. Its also heavier.


  • Fast and Quiet AF
  • Manual focus in AF mode


  • Heavier than non USM lens
  • Significantly more costly
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Which two 50mm lenses are you comparing? I don't think they actually are the same glass.... –  mattdm Dec 28 '13 at 3:24
I'm comparing Canon EF 50mm f/1.8 II Standard AutoFocus Lens AND Canon EF 50mm f/1.4 USM Standard & Medium Telephoto Lens for Canon SLR Cameras –  sevensevens Dec 28 '13 at 17:05
Those lenses are actually different internally. The wider aperture is one clue, of course, but the f/1.4 also has an additional lens element (7 elements in 6 groups vs. 6 elements in 5 groups). Canon also says the f/1.4 uses high-refraction glass for two of the elements. And it has a larger filter thread and is larger in diameter overall. Also, the f/1.8 has a plastic rather than metal mount, which shaves a bit from the price. I think your basic pros and cons are still right, but USM is only a fraction of the difference in both weight and cost. –  mattdm Dec 28 '13 at 18:07
I'm actually in the market for a 50mm (I'm still researching everything). I still in the amateur area, but wouldn't mind paying a little more for a USM. Does Canon have a 50mm prime lens with USM that is cheaper (I have a Rebel t2i btw). –  sevensevens Dec 28 '13 at 18:45
No, just that. Honestly, I wouldn't make it a deciding factor, because it is the less-good ultrasonic micromotor. You might look at the 40mm f/2.8 STM, though (nicely reviewed at dpreview; the second page compares STM vs. USM autofocus). You might also investigate the Sigma 50mm f/1.4, which uses a ring-type ultrasonic motor. (But isn't cheaper.) –  mattdm Dec 28 '13 at 19:03
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