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meniscus lens
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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