Japanese Submarine 20 x 120 mm Binoculars
Totally different construction than the 20x3 in Fig. 181. The model is encased in a thick jacket of steel and was used as a deck mounted observation binocular on submarines. The binocular itself weighs 170 pounds. 40mm thick optical windows protect the objective lenses while the eyepiece end is equippedwith a water-tight door which is sealed by tightening a hand wheeler. Thick glass and steel protect the instrument from sea pressure. IPD is adjusted by turning a lever located between the eyepieces which in turn works a geared system that rotates the prism housings. All four of these glasses are scaled-up versions of the 80mm instruments with Porro II prism systems and Erfle variation eyepieces with 60 degree apparent field angles. Figure 182 - "The photographs show this binocular with eyepiece pressure door closed and open, the pier and yoke, and the pressure element in front of objectives, 32mm thick."