Jupiter-8-1 collimation question

[randomm]

Hi all,

so, I moved my 1992 black Jupiter-8-1 from the Zorki to my newly acquired M6 and noticed that its back focusing at short distances quite a bit. I "adjusted" the focus by making it match the M6's (and my CLE's) RF at infinity by thinning the ebay-bought LTM->M adapter (rubbing it against fine sanding paper on a level surface), and now infinity matches with the RF patch (the lens screws in almost a quarter of a turn further), however, close focus is still somewhat off. At objects set and measured 1.5 meters away the RF focuses the lens to 1.6 meters according to the lens distance scale (from photos judged to be quite accurate).

I can live with the discrepancy by leaning slightly back after focusing at close distances and when shooting wide open, however, what I would prefer is to not have the RF match at infinity but match at, lets say, 1.5 meters. I have an inkling from my test rolls that it does not quite focus at infinity as yet, so perhaps I could just try to take another little bit off the adapter face and see what happens?

 

[Sonnar Brian]

Taking more off the adapter is not going to help. That will move the Cam and the Optics in equally, actual focus will not be affected. The range shown on the distance scale will change.

You need to "shim" the optics module in the focus mount. Unscrew the optics module from the focus mount, and increase the shim by ~0.1mm. Try one or two layers of kitchen foil, or one layer of the foil that seals coffee cans. You will need to reset the aperture ring when you finish, it is held in by 3 set screws.

 

[randomm]

Thanks Brian, I'll give that a go once I get a chance.

 

[randomm]

Right, I'm going through a test roll with the adjusted lens at the moment. What I have so far done is a) taking material off the face of the adapter to get lens infinity and body RF infinity to match, b) re-shimmed the lens internals so that the optical module sits slightly further out. The setup has been tested with E-PL1 via adapter and focus on E-PL1 and M6 RF now match at 1.5 metres. Only thing that is slightly off is the distance scale, when focus is at an object that is 1.5 metres away the distance scale reads more like 1.6 metres. I can live with that if, as it so far seems, I can have accurate focus at 1.5 metres with RF + infinity focus. I'll see how the test rolls turns out!

 

[Sonnar Brian]

The distance scale will be slightly off, the important thing is to align the actual focus and the RF of the camera. I collimated two J-8's this weekend. One was off by 0.15mm, the other was off by 0.8mm. The latter had a new optics module put into the focus mount before getting it.