So what went wrong? The copper tape is naturally quite soft and the small force of the camera RF roller against it, when left in one focus position for a while, would result in a tiny indent. We’re talking an almost imperceptible pit in a foil surface already only a few microns thick but it’s enough to slightly throw calibration at that point. Still good, but not good enough.
The job need to be done properly and for that I needed to buy a new spanner wrench (seen below, £10) with points at the ends. Even then, I had to grind some of it down but I finally had enough leverage to remove the collar which holds the cam – and its shims – in place.
After one failed attempt (that copper foil is like very sticky gold leaf) I managed to thicken one of the shims. This may sound an odd way of doing it but it was easier to modify the thicker of the existing shims than to add the copper foil to the surface that the shims sit on, or to the cam itself. Some very careful cutting with a scalpel and the job was done. Once put back together the calibration is spot-on without the fragility of having foil stuck to the contact surface of the cam.
A final few words on coding. As this is not a Leica lens, and especially since it was discontinued well before the first digital M (M8) with the now standard 6-bit lens coding, the digital M has no way of knowing, automatically, what lens is attached. There happens to be a screw in just the place where, if painted black, it gives the impression to the code reader that the lens is a Tele-Elmarit 90/2.8. Note from below that I had to leave a small amount to the right of the screw as reflective silver; this works perfectly and the paint stays because it’s recessed. When I set auto-ISO I have the minimum shutter speed set to 2x(focal length) and it’s nice to have this working seamlessly together with my coded lenses.