Patent ID: 6249381
Filing Date: 2001-06-19
Classification: G02B

Abstract:
An illuminating method using an optical system for forming an image of an object to be illuminated in which a light beam emitted from N (N is an integer not less than 1) light sources is divided into M light beams (M is an integer not less than 2), a light path length difference of not less than a coherent distance is given to the light beams after division, and then, light axes of these light beams are again aligned with each other to illuminate said object with the light beams of coherence reduced by this,wherein when the light path length difference from one point on said object to be illuminated to an image corresponding thereto has a standard deviation .sigma..sub.Z, the number M and the number N are set so that a relation expressed by the following expression A is satisfied: ##EQU38##where, ""W"" indicates a spectrum width of wave number of the light beam emitted from said light source.