Patent ID: 7550699
Filing Date: 2009-06-23
Classification: G02B

Abstract:
1. A focus sensing system for sensing the distance between an objective lens and a target, the focus sensing system comprising: a light source emitting an outgoing reference beam of light, wherein a portion of the outgoing reference beam is reflected from a surface of the target as an incoming reference beam, the objective lens conducting the outgoing reference beam and the incoming reference beam, and the objective lens defining an optical axis; a photodetector positioned in the path of the incoming reference beam and adapted to generate an electronic signal according to the displacement between the objective lens and a surface of the target; one or more optical elements positioned to transmit or reflect the outgoing reference beam and the incoming reference beam; and a beam block positioned to selectively block an image in the incoming reference beam corresponding to an undesirable reflection from a surface proximate to the target, whereby the electronic signal may be used to adjust the displacement between the objective lens and the target.