Nothing scientific here. You have all read how much I love Zeiss and the Nikon 28mm 2.8 AIS
Well, here is a simple uncontrolled comparison. The Nikon was shot at ISO 7200 and the Zeiss at 1800. Don't ask me why. I just picked up the camera and did my stuff. Both shot wide open. Nikon at 2.8 and Zeiss at 2.0
Anyway, here you go.
Nikon
http://zeissimages.com/gallery/4/U4I1388772690.SEQ.0.jpg
Zeiss
http://zeissimages.com/gallery/4/U4I1388772652.SEQ.0.jpg
Nikon
http://zeissimages.com/gallery/4/U4I1388772694.SEQ.1.jpg
Zeiss
http://zeissimages.com/gallery/4/U4I1388772655.SEQ.1.jpg
Nikon
http://zeissimages.com/gallery/4/U4I1388772694.SEQ.2.jpg
Zeiss
http://zeissimages.com/gallery/4/U4I1388772656.SEQ.2.jpg