I just got my 5d MkII body (not the kit). I want to replace my old 28-70 f2.8L lens because I did a test comparing it against a 24-105 f4L on my 50D and the 24-105 was much better in both contrast and sharpness.
The question is whether the ability of the 24-105 is going to be an issue with the AF system of the 5D MkII since it cannot take advantage of the center sensors which work with f2.8 or faster lenses, something the 24-70 f2.8 L lens could do. Since I often am working with people in lifestyle or sports types of situations, I wonder if that would be an issue. I like the idea of the longer reach of the 24-105, and the IS, but focusing ability is certainly the most important issue in my work.
Anyone out there have these three items and tested the results yet?
I own both lenses and a Canon Eos-1Ds III, and each lens has its strengths and drawbacks. Which you'll want depends on what you're doing. The 24 - 70 f:2.8 is optically excellent (at least my copy is), sharp right out to the corners with that nice bright aperture. On the other hand, it always seems like you're running out of zoom at the long end for a lot of subjects. The 24 - 105 f:4 is a lot more convenient with a very useful long end and the IS function, but it's not quite as good optically. The difference is subtle but real; giant prints like 24x36" will be just a bit softer with the 24 - 105. And the 24 -105 vignettes badly; this is its Achilles heel. Corners go visibly dark at anything wider than f:8 or even f:10, to the point where stitched panoramics are very problematic.
So most of the time the 24 - 70mm f:2.8 lives on my camera, which is in a bag with the 70 - 200 f:2.8 and lots of other stuff. I shoot mostly landscapes from a tripod, so the modest but real optical advantages trump convenience. On the other hand, I use the 24 - 105 mm f:4 when I'm hiking with a single camera and lens, or just walking around, or if I'm shooting people. (Umm,
photographically.) The 24 - 70 f:2.8 just isn't long enough for convenient portraits.