A range finder device for use with a controller in an optical system is disclosed in accordance with one embodiment of the invention. The range finder device comprises a transmitter to produce a first beam of non-visible radiation for intersecting a perceived object, and a receiver to detect non-visible radiation reflected from that object. The controller determines a viewing distance of the perceived object based on signals received from the transmitter and receiver. A method of controlling an optical lens system comprises utilizing a range finder device to determine a viewing distance of an object perceived through an electro-active lens and adjusting a focal length of a portion of the lens based on the viewing distance. An optical lens system comprises an electro-active lens and a controller to adjust a focal length of at least a portion of the electro-active lens based on a signal from a range finder device.