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Archive 2006 · USM vs. DC motor?

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p.1 #1 · p.1 #1 · USM vs. DC motor?

I'm thinking about getting a 70-300 zoom lens for my 20D, but I was wondering if anyone knew about the difference between getting the standard lens with a DC motor, or the Ultrasonic version. The USM costs about $30 more (retail), but is the image qualitiy any better, or does it just make less noise?

Jul 17, 2006 at 11:34 AM
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p.1 #2 · p.1 #2 · USM vs. DC motor?

It makes less noise and also focuses quicker.....

Jul 17, 2006 at 11:39 AM
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p.1 #3 · p.1 #3 · USM vs. DC motor?


I'm not sure which two lenses you're talking about. The Canon 70-300 IS does have a USM motor, but it's not quite the "real" thing, as it doesn't allow full-time manual focus, and it's not as fast or silent as the real USM. Not at all bad, though. The other 70-300 is the DO lens, which is one heck of a lot more than $30 more expensive, and most say not as good, image-wise, as the 70-300 IS (non-DO).

What lenses are you looking at? Not the old 75-300 v. the new 70-300? In that case, the new lens is MUCH better, in every regard.

Another issue is that the 70-300 IS is temporarily out of stock almost everywhere, as there was a recall of the early lenses for a fix. Expect to pay ~$550 street price, if/when you find one. I own one, and love it, but it's off for service, and should be home in a few weeks.

Jul 17, 2006 at 12:52 PM
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p.1 #4 · p.1 #4 · USM vs. DC motor?


I do know which you are talking about, and the USM version will have faster focus. As mentioned it is not a "ring USM" (such as on the 17-85), which is faster yet. The $30 is probably worth it. Better yet, spending a little more to get a used 70-200/4 would also be a good idea. It is 2x what the 75-300 costs, but the image and lens quality are easily 2x better. When the updated 70-300IS is available, that is also a very good option.

Jul 17, 2006 at 03:37 PM
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p.1 #5 · p.1 #5 · USM vs. DC motor?

Are you talking about the 75-300 4-5.6 III vs 75-300 4-5.6 III USM?

I had the III, and my mother now has the III USM. Focusing is *slightly* faster on the USM, though still quite slow in my book. Optics are unchanged, only the AF motors.

You may wish to look into the Sigma 70-300 APO - current model sells for $10-20 more than the III USM (so around $200, though it may have a slower AF drive). Optics are supposed to be somewhat better, probably the best in the class for the price range.

If you're talking about the 70-300 IS lens - that's a whole different class and the *70*-300 IS lens is supposed to be great. I would also look into the 70-200 f4L for about the same price ($550 for the 70-300, 580 for the 70-200). Both of these lenses are USM so I'm assuming you are talking about hte cheaper lenses I mentioned above.

Jul 17, 2006 at 07:49 PM

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