A meniscus lens is a lens having two spherically curved faces, one convex and the other concave, so that it has the form of a shell. A positive meniscus lens is thicker in the middle than at the edges and serves as a converging lens; a negative meniscus lens thickens toward the edges and works as a diverging lens. Very large telescopes may use meniscus mirrors, which are lightweight and require an active control system to retain their shape against gravity.
Related categories OPTICS AND OPTICAL PHENOMENA
TELESCOPE EQUIPMENT AND TECHNIQUES
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