The Russian lenses actually have a different pitch thread from the Leica lenses. Sometimes this is a problem as they don't screw down all the way without bunging up the threads. I have a 35mm Summicron Type III and a collapasable 50mm Summicron I really like they both have 39mm filter threads. I use a screw in cheap lens hood and cheap snap on plastic caps as I am notorious for dropping those things or losing them. I don't think the FIKUS works on anything but the Elmars. You can download the old catalogs from the Butkus Camera Manual site to see what fits what.