Konica M-Hexanon 90mm, adjusting focus?

[Abram]

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I recently purchased a Hexanon 90mm for my M240 and I really am quite pleased with the lens in general, however I've noticed that it tends to focus behind what I'm intending which delivers a slightly soft image overall. When I use live view or the EVF on my M240 I can nail the focus and it is an impressively sharp image. I suppose with practice I can learn where this point is and just adjust for it, but I wondered if it is possible to adjust the point of focus on the lens so that I don't always have to rely on the EVF for a sharp image. 

 

I've read that the thickness of the KM lenses are just ever so slightly different than M mount lenses and as such they can result in slight backfocus (as I'm experiencing). 

 

Any tips?

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[adan]

It was actually the Konica RF bodies that were (supposedly - never really demonstrated conclusively) a fraction of a mm different from the M spec. Distance from the front of the lens-mount ring to the film/sensor plane, so roughly equivalent to "thickness."

 

But anyway - possibly a 3rd-party Leica expert technician can adjust the cam in the lens (the brass tube inside the back opening, that moves in and out with focusing, and presses on the camera's RF roller). Leica, of course, won't touch a Konica product, and Konica/Minolta ceased support of the products in 2010.

 

I always have to stop and get my head around the RF system, but I think if it is consistently back-focusing, that means the cam is too short, not pushing far enough on the camera link, and thus the camera RF "thinks" the lens is focused closer than it actually is. If so, the two RF images should never quite merge at infinity.

[Abram]

I will have to do more thorough testing, but overall I think the lens is still very usable, it would just be nice to have it be a bit more accurate without having to rely on the EVF. I recall the same challenge with the 150mm lens on my former Mamiya 7II system. It was a bit tricky to get things in focus up close, but after having the lens calibrated to my camera it was simple.