A variable focus lens is constructed by making small changes in the equatorial
diameter of an elastically deformable lens. The lens may be deformed by radial
tension exerted in a plane generally perpendicular to the optical axis. The radial
tension may be exerted by radially acting mechanical apparatus or by means of rings
embedded or attached at the equator of the lens, whose diameter can be altered
by heating, or by imposition of electrical or magnetic fields.