05/05/2015
Canon makes two high-quality wide-angle zoom lenses for full-frame cameras, the 17-40/4L reviewed here and the Canon EF 16-35mm f/2.8L II USM, (compare prices). In the digital era, the 17-40 has been overlooked to some extent. It isn't wide enough to be dramatic on a small sensor camera such as the popular Rebel series. It doesn't offer enough of a cost savings over the 16-35/2.8L to be interesting to the folks buying the full-frame sensor cameras. Our prediction is that this lens will come back into its own when Canon brings the cost of a full-frame body down below $1200. Until then, anyone with enough money for a 5D will probably simply buy the 16-35.
Optics
The lens design is of low complexity for a zoom, with 12 elements of glass arranged in 9 groups; Canon's f/2.8 prime wide-angle lenses typically include 10 elements of glass. Three of those elements are aspherical, which improves image quality and reduces the number of elements required. Thus, contrast can be as high and flare as well-controlled as with a simpler prime lens. Distortion will be a little higher.
Maximum magnification is 0.24x at a distance of less than one foot. With a full-frame camera, the smallest object you can photograph is roughly half the size of an 8.5x11" (A4) piece of paper.
Construction
Like all L lenses, the 17-40/4L is ruggedly constructed and resistant to water and dust. The included EW-83E lens hood bayonets onto the exterior of the lens, leaving the 77mm filter and lens cap threads free. The 17-40 incorporates a ring USM motor, which enables "full-time manual focus", even when the camera/lens are set to autofocus. This is very useful when using Custom Function 4 on an EOS body, which moves autofocus to the exposure lock button on the rear. You can focus manually if desired and, at any time, push the rear button to give yourself a shot of autofocus.
Weight is 500g, which balances well with Canon's mid-priced bodies. The medium-speed prime lenses are much lighter, however, e.g., only 185g for the 28/2.8.
Alternatives
The most likely alternative to this lens is Canon EF 16-35mm f/2.8L II USM, (compare prices), which is somewhat heavier (640g) and twice as expensive. The highest quality alternative to any wide-angle zoom lens is a bag of prime lenses:
Canon EF 14mm f/2.8L II USM, (compare prices) (review), a great lens, but difficult to use effectively; dramatically wider than 17mm
Canon EF 20mm f/2.8 USM, (compare prices), the modern photojournalist's standard focal length; substantially less wide than 17mm
Canon EF 24mm f/1.4L II USM, (compare prices) (review), a great lens if you need the speed and don't mind the price and weight
Canon EF 24mm f/2.8, (compare prices), an old design; no ultrasonic motor
Canon EF 28mm f/1.8 USM, (compare prices), a reasonably new lens with ultrasonic motor; not a bad value if you want to live your life at 28mm
Canon EF 28mm f/2.8, (compare prices), an old design; no ultrasonic motor
Canon EF 35mm f/1.4L USM, (compare prices), another great low light photojournalism prime
Canon EF 35mm f/2, (compare prices), an old design; no ultrasonic motor
Canon EF 20-35mm f/3.5-4.5 USM, (compare prices), an older design; lacks L-grade mechanical construction.
If you are using a small-sensor digital SLR, such as the Canon Digital Rebel XTi (Black), (compare prices) (review), the best zoom for wide-angle drama is the Canon EF-S 10-22mm f/3.5-4.5 USM, (compare prices) (review).
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.
