Canon 24-105 4 L at 28 mm vs. Nikkor 28 2.8 manual focus.
All crops from standard jpg, no additional sharpening applied. At 28 mm, the extreme corners on the zoom suffer from some softness and from chromatic abberation. For most pictures, this will not be a problem, but clearly, when the corners matter, the Nikkor is an exceptional performer and certainly deserves a place in my bag. Already good at 2.8, but at 5.6 really superb. The barrel distortion is similar on both lenses at 28 mm and is very mild.
For some reason (I need to explore further) the light meter seems to have problems assuring consistent exposure with the Nikkor lens attached to it (or I did something wrong). I applied slight corrections (also on the previous 105 test) using curves to at least make the exposures more similar.
Make sure to open this picture at "original" format if you want to see the crops at 100%.