A control apparatus includes an acquisition unit configured to acquire optical information, a tilt control unit configured to tilt an image sensor relative to a plane orthogonal to an optical axis of an imaging optical system, and a calculation unit configured to calculate an image shift amount by a phase difference detection method based on a signal from the image sensor and to calculate a defocus amount based on the image shift amount and a conversion coefficient. The calculation unit changes at least one of a correction amount of the signal and the conversion coefficient based on the optical information and a tilt angle that is an angle formed by the image sensor and the plane.