A lens with one concave and one convex surface, so that the glass forms part of a shell. A positive meniscus lens is thicker at the centre than the edge and is a converging lens. A negative meniscus lens is thinner in the centre than at the edge and is a diverging lens. A meniscus mirror is used in lightweight telescopes, and is usually supported only by its centre as it has a comparatively thin edge.
Subjects: Astronomy and Astrophysics.