What is the construction and use of binoculars
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Answer:
Binoculars or field glasses are two telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models.
Unlike a (monocular) telescope, binoculars give users a three-dimensional (3D) image: for nearer objects the two views, presented to each of the viewer's eyes from slightly different viewpoints, produce a merged view with an impression of depth.
Binoculars have a focusing arrangement which changes the distance between ocular and objective lenses. Normally there are two different arrangements used to provide focus, "independent focus" and "central focusing":
Independent focus is an arrangement where the two telescopes are focused independently by adjusting each eyepiece. Binoculars designed for heavy field use, such as military applications, traditionally have used independent focusing.
Central focusing is an arrangement which involves rotation of a central focusing wheel to adjust both tubes together. In addition, one of the two eyepieces can be further adjusted to compensate for differences between the viewer's eyes (usually by rotating the eyepiece in its mount). Because the focal change effected by the adjustable eyepiece can be measured in the customary unit of refractive power, the diopter, the adjustable eyepiece itself is often called a diopter. Once this adjustment has been made for a given viewer, the binoculars can be refocused on an object at a different distance by using the focusing wheel to adjust both tubes together without eyepiece readjustment.