Originally posted by IgorZ ...argued that Soviet lenses were based on the contax design but have ltm mount, so he said that because of inherent design differences Soviet lenses are not sharp on Leica bodies. So his conclusion was that if you use the lens on the body for which it was designed the results will be fine. All of that to say, just curious what your experience is using Soviet lenses on Leica.
Not quite true. Without going into technical depth and history, it is enough to say that the Soviet LTM lenses have a lens-side cam helicoid pitch appropriate for a longer focal length than that typical for most other LTM lenses. When matched to a properly calibrated Soviet body,* they produce accurate rangefinder focus at all distances. However, when used with a properly calibrated Leica body, they become progressively inaccurate as the distance approaches infinity. The inaccuracy is insignificant with wide angle and normal lenses at moderate apertures (say f/3.5 and narrower), but might be objectionable with longer lenses. The J-12 is normally just fine as are most normals. I have the J-12 and J-8 in both Contax/Kiev and LTM mounts and the performance in general shooting is indistinguishable on the bodies I own.
There are extensive discussions on the Rangefinder Forum and elsewhere and also information about a hack (shims) to allow better accuracy at distance than close up. IIRC, one of the members over there will do the modification for a fee.
Steve
* The focus adjust on the body is a cam-like lever that matches the construction of the lens.