In geometry, a lens is a biconvex shape comprising two circular arcs, joined at their endpoints. If the arcs have equal radii, it is called a symmetric lens. A concave-convex shape is called a lune. The Vesica piscis is one form of a symmetrical lens; the term is also used for lenses generally.
In common usage, the term "lens" is also used to describe the shape of a three-dimensional object obtained by rotating a two-dimensional lens about its narrow axis of symmetry. Such a shape is described as lenticular.
See also 
- Eric W. Weisstein. "Lens". MathWorld. Retrieved June 13, 2005. which in turn cites
- Pedoe, D. (1995). "Circles: A Mathematical View, rev. ed.". Washington, DC: Math. Assoc. Amer.
- Plummer, H. (1960). An Introductory Treatise of Dynamical Astronomy. York: Dover.
- Watson, G. N. (1966). A Treatise on the Theory of Bessel Functions, 2nd ed. Cambridge, England: Cambridge University Press.
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