Difference btween USM and DC motor to drive the AF

Dear Users,

I'm new in the world of Canon Reflex Digital Camera. I have a Canon EOS 20D, and I'm looking for some lenses to start shoot photos.

I found lenses similar but with a difference with the USM or the DC motor to drive the AF of the lens. What is the real difference with those two systems?

I found this text in the camerahacker.com :

"The Canon EF 85mm f/1.8 USM lens has many features that I wish my Canon EF 50mm f/1.8 II lens had. It has the following features lacking in the 50mm lens: 1) the ultra-quiet, ultra-fast, and ultra-discreet USM focus mechanism; 2) the AF/MF switch that works easily, smoothly, and consistently; 3) the non-rotating, internal focusing front.
As I mentioned in the 50mm lens review article, Canon's Micro-Motor is noisy and hunts quite a bit. It is hard to be discreet in a quiet social gathering when the lens is filling the room with motor whine because it is hunting back and fort trying to obtain a focus that it never finds. Canon's USM on the 85mm lens resolved all of those problems, and I can obtain focus quickly and discreetly with confidence."

Anyone could help me? Thanks a lot!!

Welcome to POTN

That article's pretty stupid, it's comparing a $400 lens with an $80 lens. Compare with the 50mm F1.4 and they've got similar features, at a similar cost. There are threads around here every week about the 50mm F1.8 vs the 50mm F1.4, lets not start another one, but their respective prices reflect their abilities IMHO.

A better starter lens is the Sigma 24-70 F2.8, or the Tamron 28-75 F2.8. Having a zoom is great to start with, it'll do most of what you want, and you can get primes later if you need to

Hi,
welcome to the forums! The USM motor is a higher end motor, and helps the lenses focus quickly and quietly. It comes in two variants - the cheaper one I believe is called micro USM, and it still speeds up focus, and keeps it quiet, but the better version is called Ring USM - in addition to being lightning fast, it also allows you to manually focus the lens, without turning the lens into manual focus, and without damaging the motors. Sigma have a similar system called HSM. Normally the non USM motors are found on the cheapest lenses, then micro USM is found on a few consumer lenses, and ring USM is found on the prosumer to pro (L) lenses.

Hope that clears up some of the mystery.

USM is also more accurate than a standard motor.

Welcome mlphotographer ... good summaries already given above. A USM or HSM is a nice to have but won't necessarily give you a better picture than a DC motor. You need imagination, a good eye and an appreciation of 'the craft'. Without those then you're left comparing sharpness and pixel peeping while everyone else flicks through your prints with hardly a look.

When choosing a lens I personally am interested in image quality, handling and price above anything else. Up until last week I had the Sigma 24-70 2.8, that Tim mentioned, and the Tokina 12-24. Both excellent lenses that met all my criteria. Hard to beat (perhaps impossible!!) at this point in time and both lacked USM/HSM style motors. Did I care? No! Just not a priority. Did my shots suffer? No ... they all still suck Today, none of my lenses even have motors. Do I care? No!

The 50mm 1.8 is a fine little lens. It's almost like a cheap toy but it takes fine shots. I just sold my second one and am already wondering if I did the right thing. Just very valuable for those almost one off times you need a fast lens and don't have flash. That with the Sigma and Tokina would make a very fine start up package. Of course, if you're mainly interested in birding or wildlife, that would be a very bad package to have

USM is superior. If you need USM get the 50 f1.4 with USM. I would think that if the writer of the article had done their research prior to writing the article they would have made that clear.

If you need very fast focusing I realy think you want usm, or hsm if you opt for sigma.