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Binoculars, optical instrument consisting of a pair of compact telescopes mounted side by side. Since both eyes are used, the magnified image of distant objects appears to be in 3 dimensions. The magnifying power of a pair of binoculars and the diameter of the object lens (front lens) are engraved on the instrument. Binoculars marked 10 × 50, for example, will make objects appear 10 times closer and have object lenses that are 50 mm (about 6 in) in diameter. Binoculars can be adjusted to focus the image, to move the two telescopes nearer or farther apart to fit the eyes, and to remove double images.

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