21mm Top Guns

Canon 17-40mm f4 L v Nikon 17-35mm f2.8 v Zeiss 21mm f2.8

Performance at f5.6 (Zone A)

Nikon 17-35mm at 21mm / f5.6 (centre)	Canon 17-40mm at 21mm / f5.6 (centre)	Zeiss Contax 21mm at f5.6 (centre)
4.6 points	4.7 points	5 points

Full marks is the only possible response to the Zeiss 21mm at f5.6: fully resolving to the limits of the sensor. You could put a Leica APO Macro, Canon 200mm f1.8 and a Zeiss 85mm f1.2 alongside this capture and it wouldn't look any better on a 5D. One stop down, the Canon 17-40mm once again impresses, marginally outperforming the Nikon here again.

Performance at f5.6 (Zone B: Left Side)

Nikon 17-35mm at 21mm / f5.6 (mid-frame)	Canon 17-40mm at 21mm / f5.6 (mid-frame)	Zeiss Contax 21mm at f5.6 (mid-frame)
4.4 points	4.5 points	4.8 points

Barely compromised in Zone B at f5.6, the Zeiss 21mm comfortably outperforms any comparable lens at this focal length. The Canon and Nikon are practically level-pegging.

Performance at f5.6 (Zone C)

Nikon 17-35mm at 21mm / f5.6 (corner)	Canon 17-40mm at 21mm / f5.6 (corner)	Zeiss Contax 21mm at f5.6 (corner)
3.9 points	3.8 points	4.5 points

In common with most Nikon wide angles, the 17-35mm AFS f2.8 really ramps up the corner resolution from f5.6 on; you don't buy a wide Nikon for its wide aperture performance. This capture is quite respectable, though some way off the delicious rendition of the Zeiss.