Schneider Kreuznach Xenar 50/2,8 Compur Retina

Still playing with famous German factory, same mount with my other Schneider this Xenar looks similar to Schneider Kreuznach Curtagon 35/2,8 Compur Retina 
Retina was brand of rangefinder camera made in Stutgart, Germany. Later they made also SLR.
I don't know whether this lens for rangefinder or SLR yet.
According to previous owner, this lens fits on Retina IIIs rangefinder.  It's a tiny 4 element lens (with a tessar formula I guess), Some fellow from mflenses said Xenar has same formula with Zeiss's Tessar



all wide open




Look at ring bokeh below, remind me to Meyer Trioplan 100/2,8


this isn't wideopen, damn sharp