Patent ID: 7580121
Filing Date: 2009-08-25
Classification: G02B,G03F

Abstract:
1. A focal point detection apparatus, comprising: an illumination part having an illumination optical system, a condenser lens that condenses light from the illumination optical system, and a first visual field stop of which aperture is formed within a range including an optical axis of the condenser lens, and illuminating an object plane via said first visual field stop; a first image-forming part, having a second visual field stop, that forms a single intermediate image of said first visual field stop on a positioning plane of said second visual field stop based on light emitted from said object plane, and transmits said intermediate image without blocking it with the second visual field stop when said object plane is situated within a specified range containing a focused focal plane, and blocks a portion of said intermediate image using said second visual field stop when said object plane is situated outside said specified range, with the remaining portion being transmitted; a second image-forming part that divides into two parts the final image of said first visual field stop based on light from said first image-forming part; and a generating part that detects a gap between the final images of said first visual field stop that were divided into two and generates a focusing signal responsive to a locational relationship of the object plane to the focused focal plane.