Was there ever a conclusion about Pz-AF teleconverters with 6 contacts vs. 7 contacts on the camera side? I now have in front of me four Pz-AF teleconverters (Kenko 1.4x, Kenko 2x, Kenko 2x DG, Tamron-F 2x), and two have 6 contacts on the camera side, the other two have 7 (all four have 7 contacts on the lens side).
I don't know if this has been talked about before, but Bojidar Dimitrov has documented what that pin contacts are for in the different Pentax mount revisions. Here's my conjecture on the role of the sixth pin based on his pages:
Features and Operation of the Ka Mount - pin 6 looks like it's "m2" here, "m1m2 encode the minimum aperture: 00 = f/16, 01 = f/32, 10 = f/45, and 11 = f/22. The minimum aperture of f/16 is strange, since only screw mount lenses have f/16 as minimum aperture." If I understand things correctly, with the m2 contact missing, it's equivalent to "always on", so what this does is reduce the range of possible minimum apertures communicated by a lens to the body to just f/32 and f/22, which are easily the most common minimum apertures. (This would also cause mis-reporting of f/16 and f/45 min. aperture lenses when used with a Pz-AF teleconverter with the missing sixth pin, but I have no such lenses to test with so I don't know exactly what the effects would be.)
Features and Operation of the Kaf Mount - pin 6 is gone from KAF lenses, which must mean there's no such thing as a KAF lens with a minimum aperture of f/16 or f/45.
Features and Operation of the Kaf2 Mount - pin 6 is also gone from KAF2 lenses.
I'm really not sure what the significance of the missing sixth pin is on some Pz-AF teleconverters other than it seems to be an intentional revision, perhaps to more closely match a KAF and KAF2 lens mount that the body expects? Maybe a simple cost-reduction during the design revision process?
It also made me wonder about matrix metering, and if the forced "always on" of m2 could interfere with plastic (non-conductive) contacts used to enable matrix metering (talked about on the KAF-mount page):
Quote: The next question is then "how can the body distinguish between A-series and earlier lenses (even when the aperture is off the "A" setting)". Some Pentax literature points out that no matrix metering is possible with the A 50/1.2 lens. This lens is the only one whose mount contacts are all metal, i.e. its mount is identical to that of a K/M series lens. All other A lenses have at least one plastic contact. So the bodies must be looking for at least one non-conducting mount contact.
I just surveyed my lenses, and I don't see any that use a plastic contact at m2 (some have a plastic one at m1 though). I did notice that my Pentax FA and DA lenses don't seem to have any plastic contacts though (hmmm).