Covering both full-frame and APS-C sensors, the EF 17-40mm has proved popular with photographers since its launch – and for good reason
Canon EF 17-40mm f/4.0 L USM Review
So it is that the 17-40mm has a smaller maximum aperture than some cheaper lenses, even though it maintains f/4 right through the focal range. It’s also bigger and heavier than some cheaper lenses but that, of course, is inevitable given that the lens is designed to be tough enough to withstand heavy professional use.
Physically, the lens feels great: the rings for zooming (rear) and focusing (front) fall to hand and the former has a particularly smooth and precise action. All of the actions are internal so there is no extension of the lens during zooming and no rotation of the front element during focusing.
It should be noted that this is an older lens that was released in the days before digital cameras and it covers the full 35mm format, making it suitable for use with full-frame Canon DSLRs. This being the case, the resolution figures obtained using an APS-C body (EOS 40D) are encouraging as they are better than those obtained by dedicated EF-S lenses. Being critical, wide-open performance at the shortest focal length is slightly below the performance at other settings but the deficit is only slight. No visible edge distortion could be detected.
In terms of resolution there is very little to choose between this pro-spec lens and the entry-level 18-55mm. In terms of handling and build quality, however, the 17-40mm is a much better performer.