Yashica may have been the only company to start with a bayonet mount and auto-diaphragm (Pentamatic with the Y bayonet in 1959), then switch to M42 thread mounted, and return to bayonet with the C/Y mount. The TL Electro-X was the first SLR with a stepless, electronically-controlled shutter, and the first to use an LED meter, it may also have introduced battery-dependence for features other than the light meter. I believe the AX was the first camera to offer aperture-priority operation with legacy lenses.