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3

Spherical Lenses

A lens is defined as a portion of a refracting medium bordered by two
curved surfaces which have a common axis. When each surface forms a
part of sphere, the lens is called a spherical lens. There are various forms of
spherical lens, some of them also have one plane surface. This is acceptable
because a plane surface can be taken as part of a sphere with infinite radius.
(Fig. 3.1)

Fig. 3.1: Basic forms of spherical lens