A lens element whose surface is not part of a sphere. A camera lens is made of several pieces of glass called elements. Most elements have spherical surfaces, which are easier to make but cause some faults, such as spherical aberration. An aspherical element has a more complex curve. One aspherical element can correct faults that would otherwise need several spherical elements. It is often used in wide-angle and wide-aperture lenses to make them sharper, smaller and lighter and to reduce distortion.
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