If you are looking for a portrait lens that is brutally unkind to the most minor of details the planar if the one you want. It is very good at picking out the slightest little things that you might not notice. The nokton I understand is also very very sharp but as I have no practical use with one I cant say for sure on the portrait front.
Anyway, the transition between sharp and unsharp areas with this lens gives photos a nice roundness when done right. For some reason I have not been able to duplicate this roundness much with black and white, but I usually shoot color with this lens so never went in depth to see how to use this lens properly with black and white.
Some pictures to show this roundness with portraits and also the brutal detail it is capable of capturing. (by the way, sorry to those people on here who have seen these photos over and over again, I have some stuff that I need to get developed and what not as soon as I get time from stuff going on here in Chongqing)
Note, most of these shot on Fuji Superia 200 with the lens wide or widish open.
(this is one of those black and whites that to me just didnt have the roundness of the color ones, worth looking into later maybe)
This shot is very very unflattering to the subject (he didnt care, he knows he looks that way) but also you might notice the flare in the top left corner. Very rare that I see this lens flare.
So there you have it, there should be enough example there to show you basically how this lens renders transitional areas and details.