FOCUS DETECTION OPTICAL SYSTEM, FOCUS DETECTION DEVICE, AND OPTICAL INSTRUMENT USING THE SAME

Japanese Patent JP2016035524

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PROBLEM TO BE SOLVED: To provide a focus detection optical system that is compact and has excellent pupil image formation performance, a focus detection device, and an optical instrument using the same.SOLUTION: There is provided a focus detection optical system used for a focus detection device that divides a light beam passed through an imaging optical system and detects the focus state of the imaging optical system according to a relative positional relationship between a plurality of images formed with the divided light beams, and includes a condenser lens on which the light beams passed through a scheduled image formation surface of the imaging optical system, a mask that has at least one pair of aperture stops, and at least one pair of secondary image formation optical systems that forms the light beams passed through the apertures of the mask into an image on a light receiving surface of light receiving means, where the condenser lens includes a first lens having a positive refractive power and a second lens having a negative refractive power; when the focal distance of the first lens is f1, and the focal distance of the condenser lens is f, the conditional expression 0.70