21mm Top Guns

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

Performance at f11 (Zone A)

Nikon 17-35mm at 21mm / f11 (centre)	Canon 17-40mm at 21mm / f11 (centre)	Zeiss Contax 21mm at f11 (centre)
4.9 points	4.8 points	4.9 points

By f11, diffraction effects are just beginning to show themselves on a 5D with all three lenses.

Performance at f11 (Zone B: Left Side)

Nikon 17-35mm at 21mm / f11 (mid-frame)	Canon 17-40mm at 21mm / f11 (mid-frame)	Zeiss Contax 21mm at f11 (mid-frame)
4.7 points	4.5 points	4.9 points

The Distagon's microcontrast enables it to appear sharper than the other lenses even here, where diffraction effects are on the verge of being more decisive to the results than any other factor.

Performance at f11 (Zone C)

Nikon 17-35mm at 21mm / f11 (corner)	Canon 17-40mm at 21mm / f11 (corner)	Zeiss Contax 21mm at f11 (corner)
4.5 points	4.3 points	4.8 points

Pretty good corners all round by f11, through the Canon 17-40mm delivers the least appetising Zone C in this company.