The first step up Canon's ladder of standard zoom lenses, at least from the kit lens supplied with the 550D and 600D, is the EF-S 17-85mm. It's better built, with a much sturdier feel than the Canon EF-S 18-55mm f/3.5-5.6 IS kit lens for those cameras.
Improvements include a metal (rather than plastic) mounting plate for fixing the lens to the camera, a focus distance scale that's tidily positioned beneath a viewing window, ring-type USM autofocus and a non-rotating front element.
On top of that, the more generous zoom equates to an effective 27-136mm instead of a mere 29-88mm. Despite its impressive credentials, the EF-S 17-85mm was originally Canon's official kit lens supplied with the EOS 50D, and it's starting to show its age compared to the newer lenses. For example, its older-generation Image Stabilizer only delivers a three-stop advantage, whereas the latest edition featured on the humble 18-55mm IS provides a four-stop benefit.
There isn't a major increase in image quality compared with Canon's relatively cheap EF-S 18-55mm IS lens, and we only noticed a marginal gain in sharpness. When it comes to chromatic aberration, this lens is actually inferior to the cheaper lens.
The EF-S 17-85mm produces awful colour fringing especially at the wide-angle end of the zoom range. It's also the only lens in the group that doesn't come with a lens hood.
Unlike Canon's basic version of USM autofocus, 'ring-type' USM enables full-time manual focus override, ideal for tweaking focus in One Shot AF, without the need to switch between AF/ MF on the lens.
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