[jeffkrol]

sorry for the technical term

the contacts are organized such that a simple sliding switch at 1/2 stop increments can update both the maximum and minimum apatures in what is called a "grey scale encoder" technically. This simple switch which reconnects the 5 data bits (pins) as focal length changes is included in the lens.

We crossed (my edit and your post) so see last paragraph above. Still not sure of where the new data goes. The 3-2 pins are strictly mechanical and un alterable except mechanically. Have to go, will think about this more later.
Again a pin code for 5.6-22 does not exist.
Thanks

[dlacouture]

Worse still : the 18-55 is a 3.5-22/5.6-38 !
And 5.6-38 does not exists...

So, aperture seems to be transmitted through the Data pin on very recent lens, after all...

[newarts]

Now, concerning the PK-m lenses, I read somewhere an useful trick : drill a second locking hole before the original one in order to lock the lens partway in the mount, so the aperture actuator doesn't push yet the aperture lever of the lens... This way, the lens will work like a m42, but will still be able to function as before if you use the original locking hole instead of the new one... Pretty neat, huh?

Indeed! Plus, if the "A" contact is made & you e-dial in f1.2, the camera does P-TTL ok regardless of where the aperture is preset.

It is like an m42 regarding aperture and uses P-TTL for flash. I tried it and it works ok.

Might it be worthwhile altering the camera mount so it thinks all lenses have "A" capability? That way, K lenses with the extra pin-lock-hole can use P-TTL too.

I may try this to make using my m42's useful with P-TTL (I have no actual K's.)

Iowa Dave

[jeffkrol]

Worse still : the 18-55 is a 3.5-22/5.6-38 !
And 5.6-38 does not exists...

So, aperture seems to be transmitted through the Data pin on very recent lens, after all...

Ran into this statement:
Greg mentions that the flash will still show P-TTL but works as a TTL flash. Michael informed me that on some bodies with some lenses, this does not work, as the camera will still know the aperture even if the lens is off the A-position. I do not have a P-TTL flash to test further.
jr-worldwi.de: Photography: Technic
Seems to imply another way to get aperture other than the pins.....
Actually I guess they believe this as well......
We assume that this phenomenon is due to data being transmitted across the P-KAF mount's digital port. Obviously, some auto focus lenses use this to transmit precise aperture data, even if the lens is off the A-position. My Pentax DFA 100 Macro does NOT do this. If a lens does it, this means that the trick does not work. You'd need to cover the digital port with thin plastic tape or so. However, I doubt many will do that. For those intersted, please visit Bojidar's Pentax page in the section about the KA-mount and KAF-mount. More info on this interesting topic is very welcomed!