Plano-Concave Lenses diverge light. One side is flat, the other side is concave. its focal length is negative. Plano-Concave Lenses are ideal for beam expansion applications, light projection, or focal length of expansion.

Choosing the right lens shape is critical in order to minimize the optical aberrations. Multiple lenses can be used where one singlet can cancel the aberration caused by another. Generally, when working at or near infinite conjugate (collimated light on one end of the lens), a plano-concave lens or achromatic doublet lens will work best. When working at finite conjugates close to 1:1 ratio, a bi-convex/concave lens would be more ideal. Sometimes using two lenses at infinite conjugate back to back provides even better performance at conjugates near 1:1.