The Jupiter-8 is a Sonnar formula lens, based on the pre-war Zeiss Sonnar. I've used Jupiter-8 lenses made as early as 1952 and as late as the late 1980s. They have all been good. as with the other Russian lenses- they are made to the Zeiss standard, and benefit from being shimmed for best focus on the Leica. These are with a 1964 lens, in a focus helical modified for close-focus to 0.7m.