Jupiter 9 M39 vs M42

I have both; I like the silver M39 model better because it looks good on the camera! I suspect that IQ will depend more on the (good or bad) treatment that the individual samples have received than anything else.

Either is easily adaptable to m4/3.

 

Would the M39 be significantly smaller? M39s are rangefinder lenses whereas M42s are for SLRs and need to sit further from the film plane.

 

The M39 version, M42 version, and Contax/Kiev version have the same optics. The M39 version is longer.

If you can find a gently treated 1950s J-9, optically better. My 1958 J-9 is as sharp as the Nikkor 8.5cm F2.

On a u43 camera, no problems with focus. On a Leica, the J-9 is made to the Zeiss standard and usually needs to be adjusted for use.