A lens with a curved, non-spherical surface. Used to reduce aberrations and enable a more compact lens size. Aspherical lenses minimize coma and other types of lens aberrations, even when used at the widest aperture. They are particularly useful in correcting distortion in wide-angle lenses and help contribute to a lighter, more compact design by reducing the number of standard (spherical) elements necessary. Aspherical lens elements correct these distortions by continuously changing the refractive index from the centre of the lens.