Focus detection apparatus, image pickup apparatus, image pickup system and focus detection method

摘要: A focus detection apparatus which includes an image pickup element having first and second photoelectric conversion elements sharing a lens, wherein the perform of images passing through different exit pupils optical system so as to output signal used for focusing by phase difference method, shift amount calculator performs correlation calculation using each values obtained independently from calculate amount, defocus calculates multiplying coefficient, coefficient correcting portion corrects in accordance with value or element.