Doppelfernrohr D.F. 12x40, manufactured by Carl Zeiss, in 1912.
This is the military version of the civilian model called "Teleduz".
On the right ocular plate are indeed the following information "D.F. (Doppelfernrohr), 12x (Magnifications), 308250 (Serial Number).
On the left ocular plate there is the logo of the manufacturer, Carl Zeiss Jena.
The conservations conditions are excellent: all the mechanisms are running smoothly and properly.
The vision is clear, sharp and collimated. There is its original neck strap.