Patent ID: 7289655

Claim:
A method to inspect an illumination optical device by detecting a luminous flux emitted from a light source through the illumination optical device to inspect optical characteristics of the illumination optical device, comprising: forming an optical image of the luminous flux emitted through the illumination optical device onto a projection plate on which a parting frame is formed in association with an illumination region of the illumination optical device; capturing, by using an image pickup device and an image capturing device, the optical image formed by the optical image forming step; acquiring a luminance value of the captured optical image; acquiring a region, where the luminance value among the acquired luminance values is a preset luminance threshold value or more, as the illumination region of the optical image; calculating an illumination margin on the basis of the acquired illumination region, which indicates the allowance of the illumination region with respect to an illuminated region, and the illuminated region defined by the parting frame; calculating the amount of a difference between centers on the basis of the center of the illumination region obtained by the illumination region acquiring step, and the center of the illuminated region obtained by the parting frame; and determining whether the illumination optical device is non-defective or defective on the basis of the calculated illumination margin and the amount of the difference between the centers.