Canon EF 17-40mm f/4LUSM

HANDLING: Light.compact and with a reassuringly solid feel. Focus and zoom controls are smooth and nicely weighted -excellent.just as you would expect from a Canon L-grade lens.

FEATURES: Ultrasonic (USM) focusing, weather proofed construction, and inside 12 elements in nine groups take care of the imaging, including exotic glass and aspherical surfaces. Canon’s L-grade lenses come with particularly good lens hoods, robustly made and lined with black Hocking for the best Hare resistance. It’s unusually large, though, which is a good thing in terms of shading.but takes up more space in the bag. Filter size is 77mm, in common with many pro-spec lenses.

AUTOFOCUSING: Canon’s USM rarely disappoints-always fast, smooth, quiet and accurate. Full marks.

PERFORMANCE: Canon’s EF17-40mm follows a traditional pattern for sharpness. Unlike some others here that have very high levels right from maximum aperture, on full-frame this lens meets our very good rating at f/4, then jumps right into the excellent zone from f/5.6 and holds on to it, only starting to dip slightly with the inevitable effects of diffraction at f/16. Much the same pattern is reflected on APS-C only with the higher resolution demands of the smaller format pushing the numbers down. Overall the standard is very high at most commonly used apertures. If you’re looking for micro-detail, in the peak resolution test at MTF 20%, the Canon scored in the middle of this group with 110 lines-per-mm at f/8, rating excellent.

Aberration control is typical of all super-wide zooms, with significant barrel distortion and vignetting, particularlyl7mm at f/4. While this is very much par for the course with super-wide zooms, compared to longer focal length lenses it rates as a relatively poor-to-fair performance on full-frame. On stopping down, however, and on the smaller APS-C format, vignetting figures are dramatically improved as you’d expect, though distortion still remains an issue at wider settings. Also at the higher end of the scale is chromatic aberration, but the good news is that all these things can be either substantially improved or eliminated in post-processing, or even in-camera these days so the reality is not too bad at all.

VERDICT: Launched ten years ago, the Canon 17-40mm is still a great lens. It’s about the cheapest L-grade lens you can buy, which means it’s built like a tank and features that red ring and therefore is coveted by those with gear acquisition syndrome. Optical performance is slightly bettered by more modern designs, but that’s really only at f/4. It’s still very usable at that aperture, and from f/5.6 through to f/11, performance is excellent at all focal lengths.

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