What is 'USM' on Canon Lenses

[Guest]

As one of the few Pentax users that frequent these forums can someone briefly give an answer to the question in heading of this thread. Not that I am contemplating changing horses just yet - I like the look of the 450d and might possibly get one to compare with my K10D before any final decisions.

[Pol]

Re: What is 'USM' on Canon Lenses

As one of the few Pentax users that frequent these forums can someone briefly give an answer to the question in heading of this thread. Not that I am contemplating changing horses just yet - I like the look of the 450d and might possibly get one to compare with my K10D before any final decisions.

I thought it stood for Ultra Sonic Motor . the thingy that makes the lens zoom silently. No doubt some Canonite will correct me if I'm wrong.

Pol

[Ian]

Re: What is 'USM' on Canon Lenses

I thought it stood for Ultra Sonic Motor . the thingy that makes the lens zoom silently. No doubt some Canonite will correct me if I'm wrong.

Pol

Yes, USM is a 'ring' motor technology pioneered for the use mainly in autofocus lenses. Unlike Pentax, Canon decided that the AF motor for each lens should be in the lens and not in the camera body connected to the lens via a driveshaft. USM motors use ring plates that are vibrated at high frequency so that they generate a rotational force. Instead of small micromotors, these ring motors are almost the width of the lens barrel. As the frequencies of these vibrations are beyond our our audible limits, the lenses are practically silent when focusing. They also focus precisely and typically move in one single movement to lock focus. Most other manufacturers' AF systems need several distinct movements to lock focus. Not all Canon lenses use USM. Cheaper EF-series lenses sometimes don't.

Pentax is actually introducing sonic drive lenses as you may well be aware, but only for high-end (expensive) models so far. Nikon started off like Pentax using the drive shaft method but is beginning to standardise on in-lens AF motors and the D40, D40x and D60 will only autofocus with such lenses. Olympus has had in-lens AF motors since the inception of the Four Thirds system, but has only recently implemented its own Supersonic Wave Drive (SWD) AF motor system and, like Pentax, only for high-end lenses at present. Minolta had selected high-end sonic AF lenses some time ago, but most Minolta and now Sony Alpha lenses are like Pentax ones, operated via a drive shaft from a motor in the camera body.

I personally believe that Canon, with its USM lenses, has the best performing AF system and by some margin, though there have been some teething problems with some newer Canon models, noticeably the new EOS-1D models, because of a manufacturing problem.

Ian

[Guest]

Re: What is 'USM' on Canon Lenses

Thank you Pol and Ian for your anwers to my query. Particularly Ian for the lengthy explanation of both engineering features and also the potted history of development by various camera manufacturers.

[Pol]

Re: What is 'USM' on Canon Lenses

Thank you Pol and Ian for your anwers to my query. Particularly Ian for the lengthy explanation of both engineering features and also the potted history of development by various camera manufacturers.

I'll second the applause for the explanation for Ian. I didn't know all of that interesting stuff.

Thanks Ian.

Pol

[Pops]

Re: What is 'USM' on Canon Lenses

I'll add my thanks to Ian for that information