You can compare shots of the same image right here, as long as that image is an ISO chart.


You can find that here. At 17mm the 17-85 has more CA. At higher lengths, 17-85 is significantly less sharp. And of course, it's variableaperture means it cannot perform very well in low light, and outright can't produce the same shallow DOF as the 17-55 can. It does give you a bit more reach, but if you want that reach, don't mind the variable aperture, look into the 15-85 as it looks to be a much sharper lens... though I'm waiting for Bryan's much more informed review.