21mm Top Guns

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

Performance at f2.8 (Zone A)

Nikon 17-35mm at 21mm / f2.8 (centre)	Zeiss Contax 21mm at f2.8 (centre)
3.6 points	4.7 points

The Canon 17-40mm isn't ready to join the party yet at f2.8, but the Contax 21mm is ravishingly fine at its widest aperture. Amid other company, you might call the Nikon 17-35mm f2.8 is serviceable – add a bit more wide radius USM and go with it – but against the Zeiss it's plain ugly.

Performance at f2.8 (Zone B: Left Side)

Nikon 17-35mm at 21mm / f2.8 (mid-frame)	Zeiss Contax 21mm at f2.8 (mid-frame)
3.9 points	4.6 points

At most focal lengths, the Nikon displays an uneven field of focus; at this aperture it's actually sharper in Zone B than in the centre of the frame. The Zeiss 21mm exhibits a subtle but sensor-readable degradation of resolution 10mm from the sweet spot.

Performance at f2.8 (Zone C)

Nikon 17-35mm at 21mm / f2.8 (corner)	Zeiss Contax 21mm at f2.8 (corner)
3 points	4.0 points

An equally wide gulf is evident in the extreme corner. It would take very little post-production to spruce up the Contax prime's capture to a high standard, whereas the Nikon zoom is beyond redemption. In its favour, we should note that the Zeiss 21mm suffers much stronger vignetting than the Nikon 17-35mm – but this is such an easy (and non-deleterious) fix, it hardly seems fair to award a significant penalty on the scorecard.