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a binocular, periscopic optical instrument. A telestereoscope consists of two optic tubes with eyepieces, a mounting, a graduated circle, and a tripod; it has a magnification factor of 10 to 20. The stereoscopic base line—the distance between the objectives—is adjustable to a maximum of 75 cm and is responsible for the stereoscopic images produced. Tele-stereoscopes are used from concealed positions to observe enemy activities, spot shell bursts, and study the terrain. Vertical and horizontal angles are measured by means of a reticle located in the right eyepiece. Some telestereoscopes are equipped with movable lens rings mounted on the eyepieces, which make it possible to make observations with or without a gas mask. The graduated circle and the reticle are illuminated. The magnification factor of 20 is achieved with the aid of an auxiliary lens.