Found this excellent article by Robert J. Rotoloni, about one of the biggest ripp-offs of the history of optics design, the Nikkor 50mm f/1.5.
Post-war Zeiss (1950) claimed that product was a direct and shameful copy of their Sonnar, a few months later of production, Nikon "re-designed" the optic and the 1.4 was born, with alot of trades in out of focus areas for sharpness. Later in the sixties, I've been told, they re-designed the optic once again, adopting at the time, a planar design.
Zeiss Sonnar 50mm f/1.5
Nikkor 50mm f/1.5
Nikkor 50mm f/1.4