Originally posted by ptx101 I have had my K-x with the two lens kit (18-55 & 55-300) for a couple weeks and love it. Now I want to try using the older Pentax manual lenses. I ordered a lens online that was described as "Pentax-A 50mm 1:2 SMC Lens" which I would believe is the lens referred to in the forum's lens database as "SMC Pentax-A 50mm F2". My understanding is that this lens will mount on the K-x with no adapter plate required. I believe all I have to do is set the lens aperture ring to the A position and the camera will adjust the aperture and I will need to focus manually. Do I have this right?
Also, I remember reading somewhere that some lenses may short out the electrical contacts on the K-x body and - presumably - damage it. Is that true? If so, when do I have to worry about that?
Thanks for any help!
Short answer Yes the lens will work as you described
Longer answer
The aperture coding of the pentax lenses is achieved by 6 contacts, starting from the lens locking pin. aLL of these pins they are either open or shorted to tell the camera whether a lens is in the A position (third pin from the locking pin, and recessed on the camera body so a non A lens does not contact it) , AND WHAT THE MAXIMUM AND MINIMUM APERTURE ARE
The 7th pin and last one is for data feedback from the auto focus lenses, and if shorted to the lens mount tells the camera that a non AF lens is attached. this , on some bodies needs to be shorted for non AF lenses to achieve focus confirmation.
Regardless all 7 pins on the lens mount are OK to short because they are designed to be shorted to the lens mount in certain conditions including a lens being put on or off. There is no requirement to turn power off when dismounting lenses is there? even if there was, no one would accept a camera damaged by such an innocent action.
What I can't comment on is the two power pins for the KAF2/KAF3 mount that are recessed in the mirror box. One of these supplies power for the SDM, the other , I am only guessing is for control. I don't know how they would behave if shorted, but there is NO issue at all in shorting any or all of the pins on the face of the mount.