Canon 17-40mm f4 L Re-Evaluated

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

Performance at f16 (Zone A)

Nikon 17-35mm at 21mm / f16 (centre)	Canon 17-40mm at 21mm / f16 (centre)	Zeiss Contax 21mm at f16 (centre)
4.7 points	4.7 points	4.8 points

All lenses are now clearly diffraction-limited in their resolving powers, but again the Zeiss has a little extra magic and sparkle thanks to its 'drawing' style.

Performance at f16 (Zone B: Left Side)

Nikon 17-35mm at 21mm / f16 (mid-frame)	Canon 17-40mm at 21mm / f16 (mid-frame)	Zeiss Contax 21mm at f16 (mid-frame)
4.6 points	4.7 points	4.8 points

The Canon 17-40mm L here gets a little payback for its absence at f2.8: across the frame it's a little better than the Nikon 17-35mm f2.8.

Performance at f16 (Zone C: Near Field)

Nikon 17-35mm at 21mm / f16 (corner)	Canon 17-40mm at 21mm / f16 (corner)	Zeiss Contax 21mm at f16 (corner)
4.4 points	4.6 points	4.8 points

. . . especially in the near-field , where it has been outperforming the Nikon for about a stop now.