While talking to Chuck West, the pro photographer who accompanied us on the cattle drive (shown here – the cowboy photographer at work), he made an interesting point about the choice of lenses he’d made for the trip. (I was on assignment from a magazine to write an article about the trip, so only taking photos in an amateur capacity.)
He uses a Canon 5D (which is a full-frame camera), and he only brought the Canon EF 24-105mm f/4 L with him. Space was at a premium, and we were going to be on horses all day, so lots of lenses (and lots of lens changing) wasn’t on.
The 24-105mm clearly makes most sense on a full-frame camera, where you could go from genuinely wide to pretty zoomed, and so don’t need an additional wide-angle lens most of the time.
On a crop body like my XT, it’s equivalent to 38-160mm, which might give you some extra reach, but isn’t actually as useful.
If you were trying to cover around the same 24-105mm range on a crop sensor camera, I guess you’d go for the Canon EF-S 17-85mm f/4-5.6 IS USM, and while it gets some pretty good reviews, its main strength seems to be versatility rather than flat-out image quality. I can’t see pros like Chuck going for it.
So even if you had a swanky new 50D, for this job you’d be carrying two lenses – maybe the pricey but good EF-S 17-55mm f/2.8 IS USM and something else for the long end.