The BSM (Binokular Stereomikroskop) is a wide range of microscopes manufactured since '20 XX.
NOTE - I'm not sure about the correct model name.
Microscope model Leitz Stereomikroskop BSM / SM - Photo 9
Microscope Index: 111
Microscope model Leitz Stereomikroskop BSM / SM
(Microscope model: Stereomikroskop BSM / SM)