The early KMZ J-12's are faithful copies of the pre-war Biogon. My 1952 KMZ J-12 has Zeiss serial numbers on the inner fixtures. Mine was $60, but required a thicker shim to focus properly. Just like the J-3 and J-8- the J-12 is optimized for Russian cameras, needs to be adjusted for the Leica.I probably should let one go and try biogon if i can made up my mind.
One final question: As I search for a 35mm lens to use on my M4 (which is still in transit), is it worth it to pay for for Leica glass vs. just going for a recent Voigtlander? I'm not asking what a collector might think. I'm talking users think about performance vs. value. One can pick up a Wetzlar Summicron in the $1500-2000 range, a Canadian Summicron in the $1000-$1500 range or a Voigtlander Ultron or Skopar in the $300-$700 range. I see no real price advantage in going fora Summarit - unless anyone knows where I can get a great deal.
It would be interesting to test them- but I'm not buying one just to test.
I did that with the Lomography Jupiter-3+, but I'm a Sonnar fanatic. Tested it, loved it, did a write-up on it...have two of them now.
Same with the 7Artisans 50/1.1- it's a Sonnar, had to have one. At $369- easy decision. If the Iberits were priced in that range, I would try one out.