Definition
A lens that has one convex surface and one concave surface, giving it a crescent-shaped cross section. Depending on which surface has the greater curvature, a meniscus lens can be either converging (positive) or diverging (negative).
Plain English
A lens shaped like a thin crescent, with one side curving outward and the other side curving inward. It still works as a lens, but its shape helps reduce certain visual distortions.
Context Anchor
Seen in descriptions of aircraft lights, instrument optics, and maintenance parts lists that identify the shape or type of lens installed.
Derivation
From the Greek meniskos, meaning 'crescent' or 'little moon.' The name comes from the lens's shape — both surfaces curve the same direction, so the cross section looks like a crescent moon.
Why Pilots Care
Meniscus lenses are used in many aircraft optical components because their shape reduces image distortion. Knowing the term helps when reading maintenance manuals or parts descriptions for instruments and lighting.
Intuition Check
Do not think of “meniscus” only as the curve on the surface of a liquid. In this term, it describes the lens shape: one side curves out, and the other side curves in.
Example Sentence 1
The landing light assembly uses a meniscus lens to focus the beam forward without distorting the projected pattern.
Example Sentence 2
Mechanics select meniscus lenses when repairing cockpit gauges because the shape reduces edge distortion at typical viewing angles.