Patent ID: 6272291
Filing Date: 2001-08-07
Classification: G02B

Abstract:
A focus detecting device for detecting a focusing state of an objective lens, comprising:a field lens disposed adjacent to a prescribed image forming plane of the objective lens and having lens surfaces which differ in shape from each other correspondingly with a plurality of focus detecting areas;a reimaging lens disposed behind said field lens and having a pair of lens parts for forming a pair of light distributions for each of different pupils of the objective lens; anda light receiving sensor arranged to receive the pair of light distributions so as to detect the focusing state of the objective lens,wherein a first area of said field lens has a first field lens part having an optical axis which coincides with an optical axis of the objective lens and having a focal length, and a second area of said field lens which differs from the first area has a second field lens part having an optical axis which does not coincide with the optical axis of said first field lens part and having a focal length, the focal length of said first field lens part differing from the focal length of said second field lens part, said focus detecting device satisfying the following condition:f1<f2where f1 is the focal length of said first field lens part, and f2 is the focal length of said second field lens part.