I was reading a Japanese blog (one of Tom A's friends I believe) last night that outlined four of the Nikkor 50's. Basically this is what he said...
1. 50/2 S Darkest of the four. Good resolution in the middle. Softer toward the edges. Few halos. Longest focal length of the four...said to exceed 50mm but not sure by how much.
2. 50/2 H Shorter focal length than the 7 element S. Resolution very good in the middle. Very good towards the edges. Overall resolution very good. More contrast than the 7 element S. Much easier to use than the 7 element S.
3. 50/2 New or Ai or K version pick your poison Basically the same as the H and all of the various versions of that lens except for better multi-coating and slight tweaking of the formula? Best resolution towards the edges of all four. Basically the same image produced with this one as the earlier versions of the 6 element formula.
4. 50/1.8 Ai long barrel version New design. Resolves very well from center and to the edges. Marginal light reduction compared to the earlier 7 element 50/2 versions. Seems to be somewhere between the earlier 6 and 7 element versions. He says the E and the pancake are probably the same. (I have found the 1.8 New pancake to be a tad better than the E myself - informal test pics below New on left E on right).
I have yet to acquire the H, HC, Long barrel Ai, the 1.2, the Noct, the long barrel Ai 1.8, the 50/2 K, any of the 1.4's, the 45 pancake, and the old 58...but just give me some more time. lol
I have found information on the net concerning the 50/2 S that launched with the F to be scarce much to my chagrin as I own a minty copy that I really like owning. I suppose it would be best as a daylight lens or maybe for some dark motif. I should probably test all of my 50's just for fun.