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An achromatic lens is a type of lens that is designed to reduce chromatic aberration, which is the tendency of a lens to produce different colors of light in focus at different points. This is accomplished by combining two or more glass elements with different refractive indices. The most common type of achromatic lens is the doublet, which is made up of two elements, one concave and one convex. Achromatic lenses are commonly used in photography, telescope, microscope, and other imaging systems. They are also used in eyeglasses, binoculars and other optical instruments.