Hmm just back from a job using the zeiss planar 1.4 ZF 50mm... Have used it already for studio .. nice... but after using it in a very very dark theatre space the focussing becomes very difficult ... compounded by being out of practice with manual focussing. I'll try to get some comparisons up soon with the nikkor 50mm 1.4.
I use the 1.4 zeiss lens with the Nikon d2x and yes focussing is difficult. In fact the lens is very sharp at 1,4 already but the point is to focus it correctly. What has helped me a lot is buying a oculair loup.
It is not expensive ( 50$?) and really makes focussing a lot easier. I am now confident I got the focus right- even in dark conditions. I start to enjoy manual focussing again.
What I noticed about the quality of the lens- very good - better than Nikon- focal plain is perfect even at 1.4 from corner tot corner. Most lens issues gone at d2.0 - and d6,7 optimum for the whole area ( d2x 12mp)
I also have the 2.8 25mm. at 2.8 already an excellent performer- agian from corner to corner sharp even at wide open. quality only gains little further on- d9,5 optimum for the whole area.
The coating of the zeiss lenses is also the best a have seen - no flare...strong colours