This is theCanon EF 17-40mm f/4L USM lens:
EF 17-40 user reviews at Fred Miranda — A nice compilation of user opinions on this lens, with an overall rating, pros and cons.
Max Simbron’s lens of choice for basketball photography — The 17-40 is one of two lenses Max Simbron uses to shoot basketball. View this video on how to set up a remote camera, and starting at about 1:35, Max explains why he likes this lens.
Photozone.de’s Canon 17-40mm review — There are six sample shots taken with the Canon 350D / Digital Rebel XT, and the conclusion is:
The Canon EF 17-40mm f/4 USM L showed a very good to excellent performance in the lab as well as during the field tests. The lens exhibited very little vignetting and excellent resolution figures. On the downside the level of distortions could haven been a little better at the wide-angle setting. Typical for most wide-angle zooms chromatic aberrations can be visible but the problem remains comparatively low. The construction quality is next to perfect. All-in-all probably the best standard zoom for APS-C Canon EOS DSLRs at the moment.
EF 17-40 review at The-Digital-Picture.com — The review article summarizes the 17-40mm as:
Because it is a very high quality but moderately-priced ultra wide angle zoom lens, the Canon EF 17-40mm f/4.0 L USM Lens is one of Canon’s best selling lenses.
Incorporated in the review are resolution and vignetting tests. Also useful are the excellent, albeit resized, examples of photos with the 17-40 which give a good idea of the applications this lens can be put to.
Yosemite and beyond — Adam Attoun shared these wonderful set of images in this thread. The post-processing resulted in images with strong colors which might not appeal to some, but I found them to be just to my taste. All of the photos except the panorama were shot with the 17-40mm lens. The last photo is of tufas at Mono Lake.
Tips, tricks and techniques
Is the zoom ring smooth when turned? — The replies to this post indicate that the zoom ring on the 17-40 should feel smooth throughout the zoom range. You’ll need to send it back to Canon service if this is not the case with your copy.
Canon Lenses — Main page