"brianized"... That's kind of like being Lobotomized.
The cameras from the Soviet Union are built to the Contax 52.4mm "50" standard.
The Leica, Canon, Nicca, Leotax, Cosina Voigtlander R series, konica RF, and many others are built to the Leica standard 51.6mm "50" focal length.
That difference amounts to 0.1mm in the throw of the helical on the "50" going from 3ft to infinity.
BUT... different manufacturers make different assumptions about how Film sits at the focal plain, and can adjust their lenses to compensate. Most lenses experience focus shift, and manufacturers choose different F-Stops to optimize. Nikon lenses optimized for up-close and wide-open. Canon- stopped down like Zeiss did with the original C-Sonnar. Focus shift from F1.5 to F4 on a Sonnar can easily be 0.05mm, Half of that 0.1mm difference in throw.
So, my "gold standard" is a Canon III and $15 Canon through-the-lens viewer. When the lens works well on someone else's camera, I am relieved! Usually DOF of F1.5 is forgiving enough.
Now- My F1.1 Nokton and 35/1.2 Nokton: perfect on my M8, after building the RF cam of each up by 0.05mm.