About prewar Feds, it's more troublesome, as bodies and lenses were appaired one by one: they did not have the Leica specifications. So, if I want to mount a Sonnar on a Fed S, first I must control the register (28,8mm) and correct it if necessary.
All these questions are even more evident with a Sonnar 2/8,5cm. With a 2/5cm, you can use the diaphragm to be "within". With a 2/8,5cm, it's more difficult with the reduced depth of field. If you add that the origin of the Sonnars we have now is very difficult to trace...
The result: some lenses are completely unusable without adjustment. And you are very lucky if you find a 2/8,5cm Sonnar which covers correctly the whole distance range. Mine (a 1951 Jup 9) is perfect at 1,15m, but gets infinity only from f4/5,6...
If you want more, please phone!
Posted - Jul 05 2018 : 05:36:29 AM Bonjour Jacques, For my education, what is the "well-known problem" on the Fed ? Rgds Jean-Pierre