Patent ID: 7339684

Claim:
Apparatus for detecting proximity between a first object (target object) and a second object (reference object), comprising a light source ( 1 ) and a light detector ( 3 ) adapted to receive resulting back-scattered light from the reference object when illuminated from the light source ( 1 ), whereby the intensity of back-scattered light to the light detector ( 3 ) is utilized as a measure of said proximity, characterized in that the target object ( 2 ) comprises an optical device ( 4 ) having a focal plane ( 7 ) and being adapted to be illuminated by the light source ( 1 ), that the axes of the light rays from the light source ( 1 ) and the back-scattering to the light detector ( 3 ) have mutually closely adjacent and substantially parallel or coincident portions, and that said proximity corresponds to a spacing (relative position) between the target object ( 2 ) and the reference object ( 6 , 8 ) wherein the reference object is located substantially at the focal plane.