A binocular, so called because it gives binocular, and thus three-dimensional, vision, consists of two terrestrial telescopes attached to the same frame with the optical axes parallel to each other.
Each of the two telescopes making up the exemplar presented here is composed of a planoconvex lens-objective (diameter 3.2 cm, focal length 12.5 cm) and a terrestrial eyepiece; this in turn is composed of a Huygens eyepiece composed of two planoconvex lenses 2 cm apart with the flat side facing the observer, and of a erector system formed by two lenses, they too planoconvex, 2.4 cm apart.
The two eyepiece lenses have diameters of 12 and 7 mm and focal lengths of 18 and 15 mm respectively.
A diaphragm with a 10 mm hole is placed between the two lenses at a distance of 4 mm from the first. ...continues