Patent ID: 8654227

Claim:
A focus detection apparatus comprising: an image sensing unit configured to have a first pixel group which receives a luminous flux passing a first pupil area of an imaging optical system which forms a subject image, and a second pixel group which receives a luminous flux passing a second pupil area different from the first pupil area; a storage unit configured to store a first distribution function corresponding to the first pupil area, and a second distribution function corresponding to the second pupil area; a calculation unit configured to generate a first image signal by performing calculations on a first subject image, obtained from the first pixel group, using the second distribution function, and generate a second image signal by performing calculations on a second subject image, obtained from the second pixel group, using the first distribution function; and a focus state detection unit configured to detect a focus state of the imaging optical system based on the first image signal and the second image signal generated by said calculation unit, wherein said calculation unit deforms the first distribution function and the second distribution function based on the phase difference obtained from the first subject image and the second subject image.