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    A lens is an optical device that transmits and refracts light. It converges or diverge the beam of light. A single lens consists of a single optical element whereas a compound lens is an array of simple lenses with a common axis. Compound lenses are useful because it allows more optical aberrations to be corrected than is possible with a single element.  Elements which refract electromagnetic radiation outside the visual spectrum are called lenses as well.

    Lenses are classified by the curvature of the two optical surfaces. The different types of lenses are listed below in the table:

    Biconvex Both surfaces are convex
    Plano-convex One surface is concave and the other is convex
    Positive meniscus One surface is concave and the other is convex
    Negative meniscus One surface is concave and the other is convex
    Plano-concave One surface is flat and the other is concave
    Biconcave Both surfaces are concave


    The focal length of a lens in air is calculated from the lensmaker’s equation below

    P = 1/f


    P is the power of the lens

    f is the focal length of the lens

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