Abstract: There is provided a focus detection device including a phase difference acquisition unit that calculates an amount of deviation between light-reception amount distributions of a pair of light-receiving element groups arranged in a predetermined direction perpendicular to an optical axis direction as a phase difference, a conversion coefficient correction unit that corrects a conversion coefficient, representing a ratio of an amount of focus deviation in the optical axis direction to the phase difference when shapes of the light-reception amount distributions are same, according to a degree of discrepancy between the shapes of the light-reception amount distributions, and a defocus amount generation unit that generates the amount of focus deviation as an amount of defocus based on the corrected conversion coefficient and the phase difference.

Abstract: There is provided a focus adjustment device including an image sensor including a plurality of phase difference detection pixels that each perform pupil division of a photographing lens, a correction value acquisition unit for acquiring a correction value for a focus position in a spatial frequency of a subject which is obtained by the image sensor, and a focus adjustment unit for adjusting a focus position of the photographing lens based on the correction value acquired by the correction value acquisition unit.

Abstract: There is provided an image pickup apparatus including an image sensor including a plurality of phase difference detection pixels that each perform pupil division of a photographing lens, a gain acquisition unit for acquiring a gain used to correct an output of the phase difference detection pixels, and a correction processing unit for correcting the output of the phase difference detection pixels using the gain acquired by the gain acquisition unit.

Abstract: An image pickup system includes an image pickup apparatus and a mount adaptor that adjusts a flange focal length between the image pickup apparatus and an interchangeable lens. The mount adaptor includes a phase-difference focus detection unit that can output a first phase-difference focus detection signal, and an optical device that separates first incident light into second and third incident light. The first incident light is transmitted from the interchangeable lens. The second incident light enters the image pickup apparatus. The third incident light enters the phase-difference focus detection unit. The image pickup apparatus includes an image pickup device that can output a second phase-difference focus detection signal, and a controller that selects either of the first phase-difference focus detection signal and the second phase-difference focus detection signal on the basis of satisfaction of a predetermined condition and performs focusing.

Abstract: An image pickup system includes an image pickup apparatus and a mount adaptor that adjusts a flange focal length between the image pickup apparatus and an interchangeable lens. The mount adaptor includes a phase-difference focus detection unit that can output a first phase-difference focus detection signal, and an optical device that separates first incident light into second and third incident light. The first incident light is transmitted from the interchangeable lens. The second incident light enters the image pickup apparatus. The third incident light enters the phase-difference focus detection unit. The image pickup apparatus includes an image pickup device that can output a second phase-difference focus detection signal, and a controller that selects either of the first phase-difference focus detection signal and the second phase-difference focus detection signal on the basis of satisfaction of a predetermined condition and performs focusing.