Here my summary. Sorry for not posting pics, it is a heavy task for which I have not found elegant solutions (not having any site of my own).
Test scene : a kitchen corner at about 1.0m. The preferences expressed below therefore apply to 3D subjects, not to flat subjects. Backlighting and flare resistance were not tested. And night shots are another completely different subject.
The camera was a D800, so it may exacerbate differences that would remain unnoticed on a D700 or Df.
All tests were done using LV focus, so focus shift did not arise. From manual focus adjustments performed, I'd say that the 50/1.2 is most prone to focus shift. I also suspect (from relatively frequent misses in practice) that the 50/1.4 SC shifts focus to the rear. On the other hand, it delivers enough keepers; MF uncertainty (moving subject, moving operator) exceeds the shift values, so the statistics are not dramatically affected.
With all other lenses, focus shift seems to be a non-issue.
Comparisons were done in Lightroom, using the X/Y comparison function. This is indeed very difficult to share here...
50/1.4 SC vs. all others ______________________
The 50/1.4 SC is an "it" lens. It is least sharp and less contrasty wide open, exhibits more nervous bokeh, and somewhat more distortion (only the 50/1.2 beats it) and vignetting. Its colors are cooler. From 2.8, it is excellent in the center, as all others would be too, at least when tested on the Df (16 Mp sensor). I cannot mount this non-AI lens on the D800, so comparisons end there.
On the other hand, in real photography life, this lens does not disappoint. Even the wide apertures are usable for all sorts of "artistic" effects, and the center is very sharp already at f/2.0
The 50/1.4 SC exhibits significant bleeding (on night shots) and a crazy bokeh on bright backgrounds, reminding some "fauvist" paintings.
My copy is a late, multicoated version (manufactured 1974-1975); if you can find one for a low price, do not hesitate, the reward will easily exceed it. The handling is also excellent... on Df (reminder: non-AI!).
50/1.2 AI vs. 50/1.2 AIS ______________________
At all apertures from 1.2 to 4.0, they are virtually identical. Differences may be due to slightly changing lighting conditions, and sample variation (centering). It seems that the AIS colors are slightly warmer, and the contrast may be very, very slightly higher. This hints at modified coatings. There are no obvious differences in vignetting at the chosen focussing distance.
50/1.4 AIS vs. 50/1.2 AIS ___________________________
At 1.4, the 1.4 is distinctly sharper over most of the field. Accordingly, the bokeh is more nervous (more outlining, with green outlines in the background owing to LoCA). The 1.4 also exhibits lesser purple fringes on shiny cutlery edges for instance. The 1.4 vignettes more, as one would expect. It is also likely that the 1.2 has some forward field curvature (towards the camera), at least if compared with the 1.4. The 1.2 is slightly warmer.
At 2.0, both are similar, but for the vignetting, still higher with the 1.4. The 1.2 exhibits distinctly more lateral CA that can of course be corrected. The field curvature difference is still apparent.
At 2.8, vignetting levels out, and bokeh is roughly the same. The 1.4 is still a tad sharper. No changes in field curvature differential.
At 4.0, the only remaining, significant difference is the considerable lateral CA of the 50/1.2. Once CA is corrected, I still have the impression that the 50/1.4 is slightly sharper in the center, and possibly elsewhere too.
50/1.4 AIS vs. 50/1.8 AIS ___________________________
My 50/1.8 is a recent version, plasticky and with minimum focussing distance greater than 0.6m, so not the best choice, but for the chosen scene, it does not matter. I also got a 50/1.8 AI, which is better in both respects but with damaged coating, so it is used as a paperweight.
At f/2.0, colors and vignetting seem about the same. Center sharpness for the 50/1.4 is better; the 50/1.8 is still marred by some haze. Bokeh is similar in shape and tint (such as green outlining in the background), but the 50/1.8 has more outlining. The 50/1.8 seems to exhibit slightly less LoCA in the foreground; the 50/1.4 has more purple fringing, where the 50/1.8 has rather blue fringes on shiny parts.
At f/2.8, the overall pictures are hard to tell apart. The 50/1.4 still has the very slightly better center sharpness. The actual FL of the 50/1.8 is also slightly longer. The bokeh is now about the same (both lenses by the way have a 7 straight blade diaphragm, so you won't expect more differences on stopping down).
At f/4.0, differences narrow further down. I still see slightly better center sharpness with the f/1.4 lens.
50/1.4 AIS vs. 50/1.8 G ________________________________
At f/2.0, and to my surprize, both lenses are very close. Center sharpness of the 50/1.4 might be slightly better, but the 50/1.8 G delivers better edges and a more homogeneous field. This remains to be checked with a flat subject. Bokeh is similar, with maybe a tad more green LoCA with the 50/1.8 G. On the other hand, the cutlery is "cleaner" with the 50/1.8 G, so globally it is a tie.
At f/2.8, differences vanish. Strangely, the 50/1.8 G seems to have a lesser DOF.
At f/4.0, the 50/1.8 G has more contrast and takes over, if perceived sharpness is the criterion.
50/1.8 G and Zeiss 50/2 __________________________________
At f/2.0, the first thing you notice is the relatively warmer Zeiss rendering. In my opinion, the 50/1.8 G is more neutral, so let's call the zeiss "yellowish". Center sharpness of the Zeiss beats everybody else, including that of the 50/1.4 AIS. I'd call that a one-stop difference...
The Zeiss has slightly less CA. Bokeh is about the same. However, its sharpness field is not flat; the corners bend to the rear. This may be interpreted as "more nervous" bokeh, where in reality background details in the corners are more in focus, in other words less blurred...
At f/2.8, center sharpness of the Nikkor catches up, so both are now comparable. What remains is the field curvature and the color temperature.
At f/4.0, field curvature and the very slight remaining CA of the Nikkor is all what tells them apart. The closest corner is now brought in focus by the Zeiss, while the Nikkor insists that no, that corner is not in the same plane. And (surprize) I dare say that the Nikkor may be sharper in the center...
Bottom line ? _____________________________________________________
All lenses are very usable. The 50/1.4 AIS has the best performance amongst MF Nikkors.
Wide open, the 50/1.8G, while very good, may not be the best, but wait until I perform night tests... or until I shoot against the light. The Zeiss is in a category of its own, given its extreme shapness wide open (and in the center) and quasi-APO, but beware of field curvature. And, as you may know, the ZF2 version which I own is, alas, nuts against backlight as soon as you stop down...
