Petri Kuribayashi 50/2 in M42 mount is sought after these days. People want the out of focus area looks like Meyer. So they called it Domiron copy. refers to the similar bokeh. Actually Kuribayashi 50/2 was made before Domiron. 1958-1960. So no way they copied Domiron (made 1966-1968)
This lens was made along with the camera, after M42 series. It use bayonet mount. You can judge these samples, is it same or close to M42 predecessor? or not.
First sample right after I opened the box, without proper adaptation, handheld in my Sony NEX5
Now, it's attached on my helicoid adapter to NEX