I have found a systematic difference for optimization of a lens on the M9 and M Monochrom, the latter has required the optics to be moved out slightly farther from the image plane. This is after adjusting many lenses for other photographer's cameras using my own M9 and M Monochrom. SO- it was not surprise to me that the J-3Plus focus is perfect on my M9 (which aslso agrees with the M240) but slightly back-focused on the M Monochrom. The back-focus is worse when using color filters, especially deep yellow through red. On a Jupiter-3 or Sonnar, a slightly thicker shim corrects the difference. This means taking the optics module out, replacing the shim, and re-indexing the aperture.
Or... Just stick a layer of Tape on the back of the Cam. I found the copper tape that usually works did not adhere to the Brass cam of the J-3Plus, but some mylar tape did. About 0.05mm after being pressed into place, focus is now perfect from 0.7m to infinity with a Yellow-2 filter through to an Orange filter.
J3Plus Test, Monochrom by fiftyonepointsix, on Flickr
J3Plus Test, Monochrom by fiftyonepointsix, on Flickr
J3Plus Test, Monochrom by fiftyonepointsix, on Flickr
Infinity Test by fiftyonepointsix, on Flickr
All at F1.5, with Y2 Medium Yellow filter.
Or... Just stick a layer of Tape on the back of the Cam. I found the copper tape that usually works did not adhere to the Brass cam of the J-3Plus, but some mylar tape did. About 0.05mm after being pressed into place, focus is now perfect from 0.7m to infinity with a Yellow-2 filter through to an Orange filter.
All at F1.5, with Y2 Medium Yellow filter.
