Patent ID: 8160437

Claim:
A focus detection apparatus for dividing a light beam which has passed through an imaging lens, and detecting a focus state of the imaging lens in accordance with a relative positional relationship between a plurality of images formed by the divided light beams, comprising: a field mask which has a rectangular opening for limiting the light beam that has passed through the imaging lens; a first focus detection optical system which divides, in a longitudinal direction of the opening or a shorter side direction of the opening, the light beam limited by the opening; a second focus detection optical system which divides, in an oblique direction different from the longitudinal direction or the shorter side direction, the light beam limited by the opening; a plurality of first focus detection regions which respectively extend in the dividing direction by the first focus detection optical system within a frame on an expected imaging surface of the imaging lens that receives the light beam divided by the first focus detection optical system; and a plurality of second focus detection regions which respectively extend in the dividing direction by the second focus detection optical system within the frame that receives the light beam divided by the second focus detection optical system, the plurality of second focus detection regions being aligned in the longitudinal direction or the shorter side direction within the frame.