Here's a tip Peter Hennig sent along that seems to make good sense. Jupiter lenses do not have any mechanism to precisely center the lens element when tightening down the lens retaining ring. This can have an adverse effect on the performance of the lens. Peter suggests the follow procedure.

First screw on the lens retaining ring so that it only just very lightly touches the lens element.

Get yourself some sort of vibrator device. I'll leave it up to you where to find a suitable one.

Place the vibrator on the outer barrel for a few seconds then tighten the lens retaining ring 0.5mm. Use the vibrator again and tighten another 0.5mm, and so on.

Continue vibrating and tightening by 0.5mm until the ring is seated tight against the lens. In the end the lens element will centered in the retaining ring. 

Peter Hennig indicates, "I have improved Russian lenses considerable by this centering method".

June 24, 2007