I have been using a Nikon 50mm f2.8 on an Axomat for some years but got a the Schneider when I upgraded to an Opemus 6 which I bought secondhand with 50mm and 80mm Componons.
When I first compared the two 50mm lenses I was very surprised to find that the Componon was "terrible". I changed to a glass neg carrier and suddenly the performance of the two lenses was more or less similar.
Is it possible that the Componon has less DOF? I thought that this was determined only by focal length and f-stop, which were identical (f5.6) in this comparrison.
BTW even under best conditions I still think that the Nikon has a slight edge i.t.o. contrast.