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A focus detecting apparatus includes an optical unit provided on an image plane side of an objective lens for detecting a focus state of the objective lens, the optical unit forming a plurality of light quantity distributions, a photoelectrical changing unit having a plurality of elements for output

A focus detecting apparatus includes an optical unit provided on an image plane side of an objective lens for detecting a focus state of the objective lens, the optical unit forming a plurality of light quantity distributions, a photoelectrical changing unit having a plurality of elements for outputting a relative positional signal between the plurality of light quantity distributions, and a circuit for detecting a focus state of the objective lens. The optical unit includes a reflecting mirror having a light condensing property for reflecting a light beam from the objective lens to form an object image on a predetermined surface, a secondary imaging lens having at least a pair of lenses for causing the object image formed on the predetermined surface to be reimaged on the photoelectrical changing unit and a pair of apertures having aperture portions respectively corresponding to the pair of lenses. When the photoelectrical changing unit is reversedly projected by the secondary imaging lens and the reflecting mirror, the elements corresponding to the direction of arrangement of the pair of apertures of the photoelectrical changing unit are arranged so that a peripheral portion of the elements is not parallel to the center of the arrangement of the elements.

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[ What is claimed is:] [1.] A focus detecting apparatus comprising:an optical unit provided on an image plane side of an objective lens for detecting a focus state of the objective lens, said optical unit forming a plurality of light quantity distributions regarding an object image by the use of lig

[ What is claimed is:] [1.] A focus detecting apparatus comprising:an optical unit provided on an image plane side of an objective lens for detecting a focus state of the objective lens, said optical unit forming a plurality of light quantity distributions regarding an object image by the use of light beams passed through different areas of the pupil of the objective lens;a photoelectrical changing unit having a plurality of elements for outputting a relative positional signal between the plurality of light quantity distributions; anda circuit for detecting a focus state of the objective lens in one or more areas in a phototaking field by using the signal from said photoelectrical changing unit;said optical unit comprising a reflecting mirror having a light condensing property for reflecting a light beam from the objective lens to form an object image on a predetermined surface, a secondary imaging lens having at least a pair of lenses for causing the object image formed on the predetermined surface to be reimaged on said photoelectrical changing unit, and a pair of apertures having aperture portions respectively corresponding to the pair of lenses,wherein when said photoelectrical changing unit is reversedly projected by said secondary imaging lens and said reflecting mirror, the elements corresponding to the direction of arrangement of the pair of apertures of said photoelectrical changing unit are arranged so that a peripheral portion of the elements is not parallel to the center of the arrangement of the elements.