View Full Version : Difference btween USM and DC motor to drive the AF

21st of December 2005 (Wed), 16:23
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!! :)

21st of December 2005 (Wed), 16:33
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 :)

22nd of December 2005 (Thu), 03:52
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.

22nd of December 2005 (Thu), 03:55
USM is also more accurate than a standard motor.

22nd of December 2005 (Thu), 05:52
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 :lol: :lol: 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 :lol: :lol:

22nd of December 2005 (Thu), 07:05
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.

22nd of December 2005 (Thu), 11:11
If you need very fast focusing I realy think you want usm, or hsm if you opt for sigma.:D