Dear Vlad and Okynek
I just wanted to say that almost all designs of military optical equipment in Soviet Union in late forties and in fifties were German developments of WWii era. These military devices were copied and produced on Soviet plants or were assembled from German parts.
Say, Arsenal in Kiev produced in 1947-50 military rangefinders, artillery trench binoculars, periscopes, etc. They marked them with the Arsenal logo but all these devices were brought from Germany.
At the same time the main places where German military optics was brought are Zagorsk, Novosibirsk and KMZ. These factories got the main amount of optics connected with munition. Of course now it is very difficult to get any information about what actually was produced there in these years. Note that many documents connected with Soviet reparation politic in occupied Germany are sill under the seal <top secret>.
Here is one example
This is a Siemens gun camera from war time
http://www.ussrphoto.com/UserContent/2542015_1935.jpg
http://www.ussrphoto.com/UserContent/2542015_1937.jpgAnd here is Soviet RFK-1 from fifties:
http://www.ussrphoto.com/UserContent/2542015_1950.jpgThere are some differences but the main design is the same. I definitely know that Soviets had brought the entire Siemens factory (Beendorf) to USSR. This factory specialized on plane military equipment.
As I already said some details on your cameras are very typical for German design.
with best regards
altix