Over the last couple of years I have been considering a portrait lens for my Leica.
The top shot was a 35mm lens on a 1.3x crop Leica M8 so really close to 50mm. For full length or cropped above the knee; 50mm is a good choice. Below is a shot of Bonnie with my M10 and a 50mm Summilux, if you compare it with the top shot you can see its very similar and gives a pleasing perspective.
For head shots and close face crops, a 50mm distorts the face a little so a longer length is preferred.
I have portrait lens for my SLR and medium format gear but not for my Leica. Leica currently make two lens you would consider portrait lens. A 75mm and a 90mm.
I am torn between wanting the longer length of the 90mm and wanting the speed and easy of focus of the 75mm.
I’ll have do some testing with my SLR and zoom to get a feel of the two lengths and see what I prefer.