If the Feds and Zorkis are like my Zeiss, they have no film plane mark. However, you could guess fairly accurately. Then with the use of a ruler that measured in small inch or mm increments, and close up filters, you could correctl measure, and decide what would be the center of the lens coverage. There are then formulas to use, or if lucky, charts with the close up lenses, to tell you the proper distance.
Much easier with an SLR, but it can be done. It used to be done. I have a close up filter for my Canonet QL 17 III. I think I still have a couple of photos of flowers in my gallery to show it does work. But again, SLRs make it much easier.