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Lens, transparent substance, usually glass, having 2 opposite surfaces, either both curved or one curved and one straight, used for refraction, (changing the direction of light rays). Lenses are used in eyeglasses to correct errors of vision, in cameras to focus images on film, and in microscopes and telescopes to magnify images. The term is also used for the part of the eye that focuses light rays on the retina.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Lange, Dorothea to Lilac