Moonrise & Aurora

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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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4  
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
@chills42 Nice one! I didn't know that thread existed! – dpollitt Nov 4 '11 at 15:25
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
2  
@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
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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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2 Answers

up vote 16 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)

Downsides:

  • Higher Cost

Branding

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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