Patent ID: 8456651

Claim:
A method of detecting a focal position of a light beam, comprising: providing a focal position detecting apparatus, comprising: a planar beam generating module generating a planar light beam along a first path; an optical system disposed on the first path, wherein the planar light beam, reflected by an object, passes through the optical system along a second path, wherein the second path is a straight line path; an optical sensor disposed on the second path; and a cylindrical lens disposed on the second path between the optical system and the optical sensor, wherein an axis of the cylindrical lens is perpendicular to the second path; wherein the planar light beam passes through the optical system and the cylindrical lens along the second path before it is incident on the optical sensor, and wherein the light beam passes through the cylindrical lens to form a linear light spot on the optical sensor; determining a defocusing degree of the light beam according to a length of the linear light spot; and determining a tilting degree of the object according to a displacement of the linear light spot.