Negative meniscus lenses are designed to minimize spherical aberration. The lens consists of a convex surface and a concave surface where the concave surface has the greater radius of curvature. When used in combination with another lens, a negative meniscus lens will decrease the NA of the system. A negative meniscus lens is a common element in beam expanding applications.
An Antireflection Coating can reduce the amount of light reflected from each surface of the lens. Thorlabs BK7 Lenses are available with our standard -A, -B, -C Broadband Antireflection Coating (please see Graph tab above for coating details).