Canon 16-35mm f2.8 L v Nikon 17-35mm f2.8 AFS
Summary

No easy way to pick a winner here. But before I try, please be aware that earlier tests in this series were conducted with a Canon 1Ds II, and later ones (including this one) were made with the rather easier to please Canon 5D.

I reluctantly came to realise that the 1Ds II is wasted on the wide glass available for it. So I traded down, losing a shedload of grief along with those six million pixels. I now shoot blissfully and ignorantly within the performance envelope defined by the 5D's Xum pixel pitch.

The relatively undiscerning nature of the 5D (compared to the 1Ds II) means that the key advantage of the Nikon 17-35mm is arguably wasted on the 5D. What I can tell you is that if you trade up from a 5D to a 1Ds II, the Nikon has the resolution headroom to grow with you. The Canon won't be quite as comfortable.

Here's how they compare, point for point, the preferable lens marked in green.

	CANON 16-35mm f2.8	NIKON 17-35mm f2.8
Overall resolution		•
Wide aperture centre	•
Wide aperture corners		•
Narrow aperture centre		•
Narrow aperture corners		•
Overall contrast		•
Overall colour	neutral	slightly warm, stronger saturation
Chromatic aberration	•
Focusing (AF)	•	manual focus
Metering	•	stop down metering
Distortion (17mm)	•	mild barrel
Distortion (21mm)	mild waveform	•
Distortion (28mm)	pincushion	pincushion
Distortion (35mm)	pincushion	pincushion
Cost		•
Build quality	•	•
Zoom range	•

Variation is an issue with both; as is condition. A good sample of one will outperform a bad sample of the other. Which makes any conclusion a statement of probability rather than a verdict.

Given optimal samples, however, the Nikon is likely to be a sharper lens overall, especially at the wide end. Its resolution advantage offset by a modest CA handicap and problematic distortion in the 24-35mm range. Up at 28-35mm, however, it seems likely that the difference between them narrows, and it may even be that the Canon is a little sharper. Hard to tell from one half of a frame.

An healthy Canon 16-35mm is a steady rather than spectacular performer: pleasant colour; fairly well controlled aberrations; tolerably sharp and on the pricey side of reasonable. Of course it has all the 'normal' metering and AF functions, which may or may not be important to you.

Frustratingly, the Nikon's soft wide aperture centres mean that it can't wholeheartedly be recommended to those who need uncompromised wide aperture performance for landscapes. It is at least sweet by f5.6, whereas the Canon needs f8/f11 for acceptably sharp corners.

For not a lot more money the Leica 21-35mm is a notch above either in the 24-35mm range, but no better than the Nikon at 21-22mm. Ultimately, your choice will be dictated by the candidate's least unacceptable failing, rather than any outstanding virtue. That and your chance of finding a good sample.