Canon EF 17-40mm f/4L USM lens review: Popular high-performance optionBy Kevin Carter - Monday January 13 2014 Lens Review
Canon EF 17-40mm f/4L USM lens performance: Very good sharpness, particularly at the wider-end
The Canon EF 17-40mm f/4L USM achieves a high ranking for an ultra-wide angle lens with DxOMark score of 21 points. Peak sharpness at 15P-Mpix is perhaps a little behind the latest designs but it’s still very good. Like so many zooms, it’s better at the wider end where it has good uniformity, even wide-open.
At 35mm and above, sharpness drops somewhat at the maximum aperture, particularly in the outer field but that improves steadily when stopped down, with peak performance at f/8-11. Chromatic aberration is well reasonably controlled, particularly from 24-40mm but it’s evident in the extreme corners at 17mm. However on an APS-C camera with its smaller sensor CA isn’t an issue, and that’s pretty much the same for vignetting.