Conclusion

So what have we learned? The fact that the Zeiss 21mm is the finest of its type is no surprise. What might come as a shock if you haven’t scrutinised the MTF charts is that a healthy Canon 17-40mm f4 L is better than a Canon 16-35mm Mark I, and makes an evenly matched challenger to the Nikon 17-35mm f2.8 for the title of ‘best ultrawide zoom’. Contrary to the opinion of my local Canon dealer, the copy of this lens I bought in 2001 was not typical!

The Nikon is troubled by an uneven field of focus which may or may not be adaptor-related: the occasional misfire in this regard allows the Canon 17-40L to come very close in outright imaging terms: sharper in the centre overall but, compared to the Nikon 17-35mm, not improving as rapidly into the extreme corner with stopping down. In terms of more Subjective Quality Factors, the Canon’s drawing style lacks something of the crispness of the Nikon’s, a factor that combines with its warmer colour rendition to impart marginally less magic and sparkle to its captures.

The trouble with the near-perfect Zeiss 21mm is its waveform distortion. The shameful truth is that by the time the wrinkles have been ironed out, some of that lovely Distagon goodness disappears too: the bottomless resolution is inevitably compromised by the subtle interpolation required to fix the geometry. After correction, the images are scarcely an improvement over the Nikon or Canon zooms.

If you shoot landscapes and can live without geometry-correcting your images, there’s no question that the Zeiss 21mm is a must-have bit of kit. If straight lines frequently crop up in your corners you may well wonder – what’s the next best thing at this focal length: the 17-40L or the 17-35 AFS? The Olympus 21mm f2, or the new 16-35mm Mark II? And the answer is . . . the Contax N 17-35mm f2.8. Not because it’s ‘sharper’ than the 21mm Distagon (though it does outperform the Canon 17-40L) but because it has such a well balanced blend of virtues in the 21-23mm range. Just don’t shoot above 24mm with it!

Choosing between the Nikon and the Canon is a tough call: at f8 and f11, the Nikon is better; at f16 the Canon has the edge. The Nikon is a stop faster, but is it a useable stop? The Nikon has a more attractive rendering style, but the Canon is weathersealed and does stuff automatically. The final tally gives the Nikon the edge, but only just . . . .

Performance summary
Canon 17-40mm f4
Nikon 17-35mm f2.8
Contax 21mm f2.8

‘Sharpness’ :

77.1 / 90
77.5 / 90
85.1 / 90

Chromatic Aberration :

7 / 10
6 / 10
9 / 10

Geometric Distortion :

12 / 15
12 / 15
7 / 15

Bright Light Handling :

8 / 10
7 / 10
6 / 10

Magic & Sparkle :

10 / 15
12 / 15
14 / 15

Speed Rating :

3 / 10
5 / 10
5 / 10

Overall Rating (%) :

78.1%
79.7%
84.1%

For details about how these scores are derived, please see the rating explanation page.

For the full Canon 17-40mm f4 L v Nikon 17-35mm f2.8 showdown, please see here . . .