Lens

A lens is an optical component whos surface curvature and refractive index are designed such that the direction of light incident upon it is controlled.

Formulae exist for thin lens approximations to determine focal lengths etc.

For an object at distance d whos image is formed at d'

See also: Abaxial, Axicon Lens, Concave Lens, Converging Lens, Convex Lens, f-stop.