Conclusion: This is an exceptionally good lens and deserves it reputation, finding its place in most camera bags of professionals using Canon gear. The slightly warm colours produced by Canon L glass and the good contrast and control of other elements required for a nice lens are all there.
Pros: Consistent performance throughout the focal range., Build quality., Good value for money
Cons: Top end cameras already at the limit of this lens’ resolution., Edges drop off a bit as focal length increases.
Conclusion: If you shoot wide angle, full frame photographs with Canon cameras stopped down at f/8 and beyond, the EF 17-40mm f/4L lens is an outstanding lens. Contrast and sharpness are greatest at the wide end (20 and 24mm) of the zoom range and approach or exceed those of quality prime lenses.
Canon EF 17-40mm f/4L USM lens, (tested with cropped-frame APS-C body)
1 July 2007
Summary: The Canon EF 17-40mm may deliver spectacular ultra-wide angle coverage when fitted to a full-frame body like the EOS 5D, but offers a more normal, general-purpose range when mounted on cropped bodies like the EOS 30D or 400D / XTi.
Pros: Canon 'L' build and optical quality, Fast and quiet USM focusing motor, Constant f4 aperture throughout range, Will also work on full-frame body
Cons: Shorter zoom range than kit lens, No IS (although not particularly necessary), Overkill if not considering full-frame in future, Canon EF-S 17-85mm more flexible for most
Conclusion: It isn't lighter than the 16-35/2.8L. It isn't better quality than the 16-35/2.8L. It isn't dramatically wide on the small sensor cameras. However, if you want a high quality wide-angle zoom with a medium weight and a medium aperture, the 17-40/4L is an excellent value.
Summary: Canon EF 17-40mm verdict
The EF 17-40mm f/4.0L is one of the best lenses in Canon’s range. It brings you a taste of the truly exotic with ultra-wide coverage, while boasting ‘L’ quality all at a surprisingly affordable price.
Pros: Extreme wide angle coverage, Well-corrected at wider focal lengths, Fast and quiet USM focusing motor, An exotic but affordable 'L' lens
Cons: Zoom range too limited for general purpose, Soft corners at 40mm focused at infinity, Unimpressive macro capabilities, Light fall-off at wide angle (but expected)