The Canon EF-S 17-55mm f/2.8 IS USM ($1,179 direct) ?is the top-end standard zoom lens for Canon APS-C cameras. Rebel D-SLRs are generally bundled with the EF-S 18-55mm f/3.5-5.6 IS II ?lens that, while quite sharp, has a relatively slow f-stop, often requiring you to use the camera's flash in dimmer light. The 17-55mm lens is optically stabilized, which makes it possible to grab sharp photos at longer shutter speeds, further enhancing its use in lower light. It captures a 27-88mm field of view in terms of 35mm full-frame photography.
The 17-55mm lens maintains an f/2.8 aperture throughout its entire zoom range?capturing four times the light as the standard 18-55mm lens when zoomed all the way in. Gathering this much light requires a substantial amount of glass?the lens is 4.4 by 3.3 inches (HD) in size, weighs 1.4 pounds, and uses relatively large 77mm filters. The front element doesn't rotate when zooming or focusing, so using a polarizing filter to eliminate reflections is possible, and the lens does include a hood to help reduce flare.
Canon EF-S lenses cannot be mounted to full-frame cameras, so you won't be able to take this lens with you if you decide to upgrade to a EOS 5D Mark III ?this is one area where Nikon has an edge, as its full-frame lineup can use APS-C lenses at a reduced resolution in a special crop mode.
I used Imatest to check the sharpness and distortion characteristics of the lens when paired with the Canon EOS Rebel T4i . At 17mm f/2.8 it captures 2,039 lines per picture height, which is much better than the 1,800 lines required for a sharp photo. At 35mm f/2.8 it hits 1,952 lines, and it softens to a disappointing 1,516 lines at 55mm f/2.8. Stopping down to f/4 increases the score to 2,249 lines at 17mm, 2,222 lines at 35mm, and a respectable 1,926 lines at 55mm?you'll have to go down to f/5.6 to cross the 2,220 line mark at that focal length. Distortion is largely a nonissue. There's only 1 percent barrel distortion at 17mm and about 1.6 percent pincushion at 35mm and 55mm.
If you can handle its price tag, you'll be quite happy with the Canon EF-S 17-55mm f/2.8 IS USM?especially if you are moving up from the standard 18-55mm lens that came with your camera. Its fast aperture and stabilized design make it possible to shoot in dim light, and it delivers excellent sharpness?although you'll have to stop down the aperture at 55mm for the best performance. The lens is a bit front heavy on an entry-level body like the T4i, but will balance better when using a larger body like the EOS 7D?.
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