Bayonet lens mounts : back in the early 1970's Canon made some noise over the fact that their bayonet mount was the only prescise mount, and the only bayonet that would not be "loose" after some use.
Looking at some Exakta bodies an their lenses I have to acknowledge that, their Canon breech lock bayonet WAS better than most (and CRC-controlled machine stations took care of those 3-hands approaches....).
However, I have early Praktina bodies straight from DDR and straight from the late 1950's.
The model for the Canon breech lock bayonet was no doubt the Praktina breech lock bayonet. It's hell for strong, an intriguing concept, too bad the DDR guys dropped it.
The T-mount concept, a 42mm 0.75mm pitch, 55mm back-focus lens with adapters for most camera systems at the time, including adapters to 42mm 1mm pitch, with ca 42mm back-focus "Universal mount" is another intriguing concept.
The DDR guys was there first, the camera industri in Dresden was very inventive, and it was a pity they where locked out from the world market due to cold war politics, but with the T-mount system and the systems that followed them the japanese excelled and pretty soon had the optics market all sewed up.
I sort of collect old & interesting lenses and have concentrated on Soligor for starters, they had at least 3 separate and fully fledged lines of lenses, T-mount, T-4 and later dedicated lens mounts, and getting them all can be time consuming. Also Soligor was one of the few lens manufacturers that also was a "camera factory", in some financial moves they controlled Miranda, and after dropping the Miranda bayonet, they came out with a M42 line of camera bodies, as well as compact cameras.