I had a nice find from Russia while looking for some photo equipment: the Photo rangefinder DF (the “DF” probably stands for “Photographic Rangefinder”). It had a good price and it is just the right equipment for my Smena 8M. There was no much information about it except that it seems to be quite rare. According to fotoussr.ru it is a copy of the Smena rangefinder from GOMZ (State Optical and Mechanical Plant) produced at the MMZ (Minsk Mechanical Plant) for probably quite a limited time from 1957-1961.