You need to bear in mind that all these cameras were made to a low standard of precision due to the crudity of the machine tools used. Hence the factory relied on post manufacture manual adjustment of lens and camera body to produce a satisfactory product. If you change the lens then it is unlikely that the new combination will work properly without re-shimming. Also the pre-war Fed lenses with a minimum aperture of f/18 had a slightly different thread to the lenses on later Feds and Zorkis. You may find that the later lenses with the usual f/16 minimum aperture won't screw on properly.
Originally Posted by gflanslo