Patent ID: 7348528

Claim:
A distance measuring system for use in an optical system capable of examining a target surface and having an objective lens defining a system in-focus region, said system comprising: a light source emitting an outgoing reference beam of light, wherein a portion of the outgoing reference beam is reflected from the target surface as an incoming reference beam; a photodetector positioned in the path of the incoming reference beam and adapted to generate an electronic signal according to the position of the incoming reference beam on the surface of the photodetector; a first scanning mirror capable of controllably deflecting the outgoing reference beam and the incoming reference beam; and a reflecting knife-edge element defining a plane, the knife-edge element positioned to obstruct any portion of the outgoing reference beam on a first side of the plane and to subtend the incoming reference beam on the first side of the plane; whereby the controllable deflection of the outgoing reference beam allows selection of a point on the target surface for generating the electronic signal, and the electronic signal may be used to adjust the displacement of the target surface.