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.