Konica M-Hexanon 90mm f/2.8 – part two

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.

Author: jrhughes

Camera geek and consumer of wine.

2 thoughts on “Konica M-Hexanon 90mm f/2.8 – part two”

    1. I guess I knew by how much I needed to effectively bring the cam forward (further towards the lens mount) given the previous experiments (part one). It was a case of getting underneath the cam instead of sticking something over it. Given that the copper tape I’d bought was pretty much exactly the right thickness in just one layer, I figured I had to remove the cam and place a single layer of the copper tape underneath it, then replace it. I was aided by the fact that, for this lens, the ability to undo the ring that holds the cam down and remove the cam, was relatively straightforward. I wouldn’t try this on a Leica and I’ve no idea how your Canon is constructed, I’m afraid.

      I unscrewed the ring holding the cam in place and the cam unit came away; underneath it (connecting it to the optical cell) were several shim rings of varying thickness, the combination of which were put there to allow accurate focussing with the Konica Hexanon. This, it has been mentioned elsewhere, is very slightly different in register to Leica and so, sure enough, the lens would rear-focus with my factory-calibrated M-240. What I needed to do was add a shim (ideally) but as I didn’t have any I decided to “thicken” one of the existing shims using a layer of the copper tape, thereby effectively adding the required thickness underneath where the cam is affixed. It was easier to do this than try to stick the tape under the cam mount itself. I cut a square of copper tape, stuck the thickest of the existing shims down on it, then cut around the shim with a sharp knife, ending up with a new shim which had its original thickness plus that of the tape. Replaced all shims, including the “new” one, tightened the ring that mounted the cam and it was perfect. And it stayed that way.

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