Plano Concave Lens A plano-concave lens is an optical lens with one concave and one flat surface. It has a negative focal length and can be used for light projection, beam expansion or to increase the focal length of an optical system. Plano concave lens bend parallel input rays so they diverge from one another on the output side of the lens and hence have a negative focal length. The spherical aberration of the plano concave lenses is negative and can be used to balance aberrations created by other lenses. Similar to the plano concave lens, the curvature surface usually faces the largest object distance or the infinite conjugate to minimize spherical aberration. Applications 1. Plano-concave lenses are commonly used to divert parallel beams in instruments such as Galilean beam expanders or telescopes. 2. Plano-concave lenses are also used for beam expansion of high peak power pulsed lasers. The incident beam will be focused on a concave surface to a point outside the instrument.
