Originally posted by dcshooter
Unlike other manufacturers's mounts, the K mount (and m42 before them) have always been "open" designs, free for anyone to use (although I'm not entirely sure this is true about the modern AF design).
It is more complicated:
K-mount has always been free indeed.
KA was closed though but patents expired, which explains why Samyang can produce KA compatible glass but could not do the same for electrical F mount, they later redid early Nikon F mount lenses to AE F mount. It also explains why Canon versions still miss any electrical linking.
BTW, Ricoh and Chinon to cite those two both did their own variations of the 'electrical' K mount back in the time.
KAF is not free yet
KAF2 is not free yet and
KAF3 is not free yet either obviously.