I've narrowed down my lens choices to two - the Canon 17-55 f/2.8 or the 24-105 f/4L (to be used mainly with a 450d). I already know my focal length preferences, but am mainly wondering about differences in AF between the two. The 450d, like the 40d and later cameras, supposedly has a higher-sensitivity center AF point that functions with a 2.8 or larger aperture. How much difference will this really make in terms of AF speed and accuracy? (I'm not attempting to shoot sports or birds on the wing, mostly just landscape, but occasionally some subjects that may move around a bit, such as my dogs.) Everything I've read about the 17-55 seems to indicate it's a very sharp lens and great in low light (a big plus for me), but I'd rather have something a little longer. I'd put up with it, though, if I could expect noticeably better AF performance. (Ruled out things like the 24-70 f/2.8 because of weight and bulk.)
Thanks.........

Hi,

Photozone is a good source of information: http://www.photozone.de

Yeah, they are German but write in King's English.

Best regards
Erik

Yes, I've read the photozone reviews, as well as those at slrgear.com and the-digital-picture.com, but none really address this question, other than to mention that AF is fast and accurate in both cases. I'm sure both of these lenses have adequate AF, and I know this is a bit of a hair-splitting question to ask about lenses that no one would really consider for "action" shooting. I just wonder if the 2.8 aperture would give any noticeable edge in accuracy with a camera like the 450d. If anyone has any personal experience I'd love to hear.......

Thanks

I have no experience with the 24-105, but I have had the 17-55 for about a year and a half. It's a great lens - probably sharper than my 50 f/1.4 prime at the same aperture. Cleans up really well in DxO too. I can say that it focuses very quickly, but I don't have too many slower lenses to compare it to.

You will hear people complain about the 17-55 getting dust inside, which I assume is not a problem for any L lens. My 17-55 has indeed picked up a noticeable amount of internal dust (not surprising since I live in New Mexico). I very much doubt that the dust has any impact at all on images though.

I guess I wouldn't be too concerned about this autofocus issue anyway. The difference in angle of view between 17 and 24mm is vast. A 24 just wouldn't be wide enough for me. I shoot my 10-22 a lot, so clearly I'm a wide angle enthusiast. If you're like me, that should be a bigger factor than incremental autofocus speed.

Let me add to Misirlu's comments.

I have the Canon 10-22 and the 17-55. Both are very fine lenses. If I had to do it over again, I would buy the 10-22 and the 24-105. There is just too much overlap between the lenses that I own. The lens aperture doesn't matter to me, as these are for personal walk-around and landscape (tripod) use.

If I only had one lens, then I agree that the 24-105 on a 1.6x-crop body would not be wide enough for me.

Actually, k brings to mind a few other considerations. My 40D came with a 28-135 IS lens. That seemed like an odd lens to bundle with that camera, but it turns out to be useful every once in awhile. If I'm walking around at an event, like maybe a car show, sometimes I'll take the 10-22 for a few dramatic scene-setting shots, and then use the 28-135 for just about everything else. In some landscape situations, I need both the 10-22 and the 17-55. In fact, I need them both so much that I wouldn't mind having a second body just so I could use either one quickly.

Back in the dinosaur days of 2004, I had the original 18-55 wonderplastic kit lens on a 20D. That thing got a lot of grief from reviewers, but, it had its uses. First, in bright light, you could stop down far enough that it wasn't too bad for sharpness even in the corners. DxO took care of the remaining distortions. So it really could produce decent images. It was also small and light, and I really wouldn't have cared if it got scratched, stolen or broken. If it hadn't had a rotating front element (making filter use a pain), I might still have it. Just for high-risk situations, or when bulk would be a problem.

Honestly, these types of decisions are never really cut and dried. And, I'm sorry we haven't helped much with your original autofocus question.

I also have the 10-22 and 17-55 + a 70-200 (with a 40D). Brought these all to Europe and used the 17-55 probably 95% of the time (walk-around) and the 70-200 next most frequently, and the 10-22 <1%.

All are fine lenses, but I really do love my 17-55 - I think it is sharp and quick to focus (blows the kit lens away) and is certainly lighter and less obvious than the 70-200. The 10-22 I no longer use as often as I used to, as I am getting into "stitching", unless I want to use a polarizer for a wide scene.

Plus no dust issues that I can see with my copy of the 17-55.

But if you ever move up to FF then the 17-55 (being an EF-S) won't be usable to you so that may be a consideration in your decision.

Andrew

Actually, it is some help with my question - tells me that if it's not a big deal one way or the other to most people, it shouldn't be to me either, and should decide primarily on other factors.
Thanks