 BetterPhoto Member |
usm vs other lenses Am considering buying a Canon EOS 20D. What is the difference between 18-55 USM lens and one without USM. There is a difference in price. Thank you.
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Steven Chaitoff |
USM stands for UltraSound Motor or Ultra Sonic Motor (as Canon calls it.) Both motors power the lens' autofocus, but a USM is much, much quieter than a regular (non-USM motor.) I believe that is the only difference, but it is a considerable one when you hear it. A non-USM motor is fairly loud, like a little drill or something when the camera autofocuses. A USM on the other hand sounds like a soft, high pitched whisper. It is a much more pleasant sound, but there probably aren't too many conditions that'd really require a lens equipped with USM, so it really seems to be a matter of convenience.
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Christopher A. Vedros |
In my experience, USM lenses also focus MUCH faster than non-USM lenses. This may not apply to all lenses, but it's what I've seen in the lenses I've tried. I think it would be safe to say that with two otherwise-identical lenses, the USM version will focus more quickly than the non-USM version.
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Andrew Laverghetta |
I have a Canon EF 200mm f/2.8L lens that is USM. Granted it's an L series lens, the focus is incredibly fast due to the larger aperture, but I believe a lot of it has to do with the USM as well. The ONLY sound that the lens makes while focusing is comperable to turning the focus ring on any other lens while in manual focus mode. Another thing about USM is that NORMALLY the front lens element doesn't turn so specialty filters can be used easier, but I believe it might on the 18-55mm. Correct me if I'm wrong. Also, Canon USA didn't offer that lens in USM form until a while after the 20D was offered. It was only in Japan I believe. If you're around people with your camera long enough and the get accustomed to hearing the sound of the focus, this might alert them to your habits so the USM could help better with candids. Also, I don't think many if any places offer the non USM version of the that lens any more (18-55). I know at least B&H Photo doesn't anymore. Just the USM. Hope this helps!
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Jon Close |
There are two versions of USM: micro-USM and ring-USM. Micro-USM is used in the entry level lenses such as the EF-S 18-55 f/3.5-4.5 USM, EF 28-105 f/4-5.6 USM, EF 75-300 f/4-5.6 USM. Many of these lenses are generally offered in USM and non-USM versions. While marginally quicker and quieter than conventional autofocus motors, the USM versions are otherwise identical. The motor is connected to the focus elements through reduction gears and one needs to use the MF/AF switch to disengage the motor when manually focusing. Ring-USM is used in the mid-level zooms (like the EF-S 17-85 f/4-5.6 IS USM and EF 28-105 f/3.5-4.5 USM) and the L-series professional lenses is more advanced. The motor surrounds the focus elements and moves them directly without gearing. Ring-USM is faster, nearly silent, and enables Full-Time Manual focus (FTM). FTM allows manual focus without having to having to disengage AF with the MF/AF switch, and also gives a nice damped feel to the focus ring. There is one exception to the above. The EF 50 f/1.4 USM uses a micro-USM motor, but has the FTM feature.
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Jon Close |
picking nits - the EF-S 18-55 is f/3.5-5.6, not f/3.5-4.5.
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