I've used the 50mm Flektagon and Bronica Zenzanon (actually a CZJ Biometer) as well as Nikkor and Komura lens and the Carl Zeiss Jena lenses were just vas good.

Where all the CZJ post war lenses are let down is the quality of their focus mechanishs and the cheap natsy lubrican that dries out, or gives unsmooth travel, sometimes the aperture stop down systems are poor as well. Bronica had their own focus mount.

I use a 1950's CZJ LF Tessar lens and it's equal to late production Xenar's and nearly a stop faster.

Ian