Originally posted by rawr Hopefully auto-focus will come to Samyang K-mount soon.
Won't happen.
For it to happen, Samyang would not only have to implement the mechanism for screwdrive AF (or even some kind of SDM or however you want to call the in-lens motor-driven AF), but also to implement the electrical protocol Pentax uses on the KAF bayonet.
Implementing the mechanism would be something that has to be re-invented for other lens bayonets; Nikon also is capable to use screwdrive AF, so there might be some synergy, but Canon is fully electric ...
But the mechanism is just part of the job, the problem lies in the communication between lens and camera body.
This is completely undocumented, and 3rd-party lens makers have either to license it from Pentax (as Tamron seems to do) or re-engineer it (as Sigma does).
Tamron apparently only licensed the old screw-drive bayonet, else they'd be selling SDM lenses, and even OS lenses (yep, that's real, optical stabilisation works on Pentax cameras, as numerous Sigma lenses show).
Since Pentax clearly isn't interested in 3rd-party lenses, the 3rd-party manufacturers have just the four options:
- ignore the Pentax lens market
- only produce fully manual lenses with the KA bayonet (and hence a diaphragm ring), since this is well understood and has no undocumented parts
- try to license the lens protocol (might be connected to becoming Pentax OEM manufacturer)
- re-engineer the lens protocol (with all the nice consequences, as Sigma is currently experiencing, with mechanical and firmware issues)
Alas, it's mostly the first or the second option that today's lens makers are choosing.
In a better world, Pentax would create a licensing program for 3rd-party lens manufacturers to increase the choice for Pentax users, but quite obviously their marketing department works differently.
What Pentax does not produce (or re-badge), Pentax users don't have a need for.
(For users of telephoto lenses there is an option to obtain AF in retrofit - with the AF 1.7x Rear Converter. But that changes the effective focal length and surely changes image quality somewhat, so it's definitively not a solution for this very Samyang lens here)