The Canon EF 17-40mm f/4.0L may offer ultra-wide coverage when mounted on a full-frame body like the EOS 5D, but actually delivers a range close to a standard kit lens when fitted on a body like the EOS 400D / XTi.

To illustrate the range in practice we mounted an EOS 400D / XTi on a tripod and photographed the same scene with the EF 17-40mm at its shortest and longest focal lengths, then repeated the process a few moments later with the standard EF-S 18-55mm kit lens for comparison.

Below are the shots taken with each lens at their shortest focal lengths. With a slightly wider equivalent focal length of 27 to the kit lens' 29mm, the EF 17-40mm unsurprisingly captures a slightly wider field of view, although it's pretty close. If you want a much wider field, you'll need to go for something like the Canon EF-S 10-22mm.

Canon EF 17-40mm f/4L USM		Canon EF-S 18-55mm f/3.5-5.6
17-40mm at 17mm, f8 (27mm equivalent)		18-55mm at 18mm, f8 (29mm equivalent)

Next up came the long-end of each lens, and again below are shots taken with the EF 17-40mm and EF-S 18-55mm when zoomed-in. With equivalent focal lengths of 64 and 88mm respectively, the kit lens is clearly capable of capturing a noticeably smaller field - and this undoubtedly makes it a more flexible option for day-to-day use. The EF 17-40mm can feel a little too short as a single general-purpose lens, but it may suffice depending on your requirements and the other lenses you intend to use with it.

Canon EF 17-40mm f/4L USM		Canon EF-S 18-55mm f/3.5-5.6
17-40mm at 40mm, f8 (64mm equivalent)		18-55mm at 55mm, f8 (88mm equivalent)