The Canon EF 17-40mm f/4L USM Ultra Wide Angle Zoom Lens is an ultrawide zoom with terrific, sharp optics.
If you need a wide angle lens, but you need to zoom in on occasion to get closer to your subject, you can do it with great results with the Canon EF 17-40mm lens.
According to Canon:
A new and affordable L-series ultra-wide-angle zoom lens that's ideal for both film and digital SLRs. Superior optics are assured by the use of three Aspherical lens elements, in addition to a Super UD (Ultra-low Dispersion) glass element. Optical coatings are optimized for use with digital cameras. This lens focuses as close as 11 inches (0.28m), and offers both Canon's full-time manual focus and a powerful ring-type USM for fast and silent AF. It has a constant f/4 maximum aperture, and offers the choice of screw-in 77mm filters or a holder in the rear of the lens for up to three gel filters. Finally, it offers weather-resistant construction similar to other high-end L-series lenses.
