Could someone comment on how vital USM is on wide angle lenses, especially the 28, 24, & 20 mm? Canon makes USM and non-USM versions--since the barrel doesn't have to travel very far, from the nearest focusing point to infinity, how necessary is USM?

-- Preston Merchant (merchant@speakeasy.org), May 09, 2002

Answers

I own the 20mm f2.8USM and the 28mm f2.8. The time it takes for either lens to focus from near to infinity is virtually identical, perhaps a few milliseconds difference at most. The big question is do you mind the noise? The 28mm f2.8 can be heard quite easily; it is a high pitched gearing sound. I don't really mind the noise...

There is only one model of the 20mm, and it is USM. So, no choice to consider here...

There are two 24mm lenses: if you can afford the f1.4L, heck, buy it!! The red stripe is worth the extra thousand bucks ;^D

The difference in price between the 28mm f1.8USM and f2.8 non-USM is modest, but I chose the f2.8 because many claim it to be optically superior to the f1.8 and, so far, I am very happy with its performance (I rarely shoot wide open). The f2.8 is virtually identical in build quality, handling and noise as the 50mm f1.8 mkI, which I also own.

-- Roger S. (rashrader@hotmail.com), May 09, 2002.

Preston, I think what you are asking is what many of us have wondered, I can tell you that my 20-35L USM set at 24mm, is really not noticeably faster than my AFD focusing 24f2.8- so it may not be as useful at this wide focal length. JC

-- joe cap (joemocap@yahoo.com), May 09, 2002.

But the 20-35L wasn't USM.....

For wide-angles, I don't believe there is a huge difference in speed. Noise and FTM swing it the way of USM, and I long since resolved never to buy another non-USM AF Lens.

-- Isaac Sibson (isibson@hotmail.com), May 09, 2002.

I love the full time manual focus of USM lenses but find my 24/2.8, 35/2 and 50/1.8 focus just as fast, just as accurately as my USM 20- 35/3.5-4.5 zoom. Noise? Not much. Not enough to worry about. There might be some marginal convenience in the lenses if they were USM instead of AFD, MM or whatever. Still, it would only be marginal.

-- Lee (Leemarthakiri@sport.rr.com), May 09, 2002.

I have the EF24 2.8, EF28 2.8 and EF35 2.0. They all focus very fast but I have never compared them to the USM versions. However, I have the EF50 1.8 (MK I) and EF50 1.4 USM and AF speed is about the same. In fact, I was disappointed that the EF50 1.4 USM wasn't noticeably faster when I bought it last Fall. I have an EF135 2.8 SF with internal focus and AFD motor and it focuses extremely fast. However, I think the IF design has more to do with AF speed than whether or not it uses an USM or AFD motor.

Like the posters have said, the main benefit of USM with these lenses is silent AF and FTM.

-- Puppy Face (doggieface@aol.com), May 09, 2002.

I also have the EF24 mm lens and find the autofocus to be quick, and the noise isn't an issue. I have the EF28-105USM and don't find much difference in speed compared with the 24mm. The zoom is quieter, but the optics of the 24mm outway the slight noise. As far as which is quickest (the 24mm or the zoom at 28mm), I can't tell much difference.

Hope this helps

-- Sarah Needham (sarah.needham1@orange.net), May 10, 2002.