28mm Comparison: f4 Resolution

Here's where it all comes unstuck. The 16-35mm I received from Canon UK had come direct from their service department, complete with dated inspection dockets. However, it swiftly became evident that it was decentred. Exactly as two Sigma 12-24mm previously tested had been. From about 24mm up, the right side of each frame was defocused. Tantalisingly, the nicely sharp left edge of each shot in the series suggests the possibility that from f8-f16 the Canon may be sharper in the 28-35mm range.

At f4, there's no question that the Nikon is sharper the Canon across the frame; even though the Canon's left edges look good at smaller apertures, there is no spot in the frame where the Nikon isn't sharper here.

Canon 16-35mm/28mm f4 (centre left)	Nikon 17-35mm/28mm f4 (centre)

Looking at the right edge at f8, we see a nice sharp left side from the 16-35mm, and this on the right:

Canon 16-35mm/28mm f8 (right edge)	Nikon 17-35mm/28mm f8 (right edge)

Yet at f16, a comparison of the upper left corners is revealing.

Canon 16-35mm/28mm f8 (right edge)	Nikon 17-35mm/28mm f8 (right edge)

Close inspection of the left edges of the frame indicates that the Canon at least matches the Nikon at 28mm from f8 up. We find a similar story at 35mm....