Originally posted by Lowell Goudge
...most M42 lenses don't short this pin because their base is narrower, and as a result the focusing indication does not work...
Lowell...
Strangely, all of my m42 lenses have a wide base that fully covers the contacts. All, that is EXCEPT the Jupiter-9. It has a famously narrow base that only covers the contacts half-way (similar to the photo above). The narrow base is characteristic of most of the Super-Taks that I have seen as well as many German and Russian lenses.
As mentioned in my previous comment, the paint on my wider-based lenses is an effective insulator whereas the paint on the J-9 is not. Of my m42 lenses, the J-9 is the only one that supports "catch-in-focus" on my K10D.
In regards to focus indication...focus confirm on my K10D using the body's AF sensor (green hexagon and beep) works with all my m42 lenses regardless of the width or conductivity of the base.
Steve
(For what its worth, my K10D has firmware version 1.20. The behavior with other firmware versions or on the KxxxD series cameras as well as the K20D may be quite different.)