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Title: Fast and Sharp But Comes Up Short on the Long End
Review: Purchased last December to upgrade the Canon 17-85mm IS "kit lens" that came with my 20D. Careful testing showed this new lens to be about "one-stop sharper" over the 17-35mm range than the kit lens. What I mean by this is that the 17-55 matched the 17-85 sharpness with one stop faster aperture: same sharpness at f2.8 for 17mm as the 17-85 at f4.0. Beyond 35mm the sharpness of the 17-55 faded until both lenses were essentially equal in sharpness at 55mm. The 17-55 was noticibly softer at 55mm than at 17mm while the 17-85 was sharper at 55mm than at 17mm. So, the advantage of f2.8 and better sharpness at the wide end for the 17-55 is at least partially negated by diminished sharpness at the meager 55mm long end. The 17-85 has about the same build quality but is smaller, lighter, covers a longer focal length range and for me is a better deal at about half the price.
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