Abstract: Optical distance measuring apparatus has a focusing lens (16) directing light reflected from a target toward a detector (18), The lens has discrete or continuous zones each associated with a target distance. The area of the lens zones increases with an increase in associated target distance so as to compensate for a reduction in intensity according to the inverse square law.

Abstract: A voltage source is connected to a laser diode via a supply circuit and a control circuit serving to control current through the laser diode. The control circuit includes a transistor which is switched into conduction on the application of a threshold valued voltage. A light sensitive diode is optically coupled to the laser diode and is adapted to apply a control voltage to the transistor switch which is related to the optical power output of the laser diode, such that when the control voltage exceeds a predetermined threshold value, the transistor is rendered conductive to control current through the laser diode.