Thanks Bjørn and Frank. Well, the Naerfoto website is not too negative about it.
That 50/2 is the humblest and cheapest in my cupboard, but its performance came as a good surprise. Lacks a bit contrast (coatings...), but close-up it is better than I feared. The bokeh can be nervous owing to the 6-blade diaphragm, but I like "special effects" every now and than. All shots were at f/5.6.
Diffuse afternoon light, it was still raining.
The recessed front lens is convenient, no urgent need for a shade, unlike my 50/1.8 AIS (short nose) which I never liked that much.