A control apparatus includes an acquirer (204a) which acquires a first signal and a second signal that correspond to light beams passing through different pupil regions of an image capturing optical system, a calculator (204b) which performs a plurality of filtering processes with different bands for the first signal and the second signal to calculate a plurality of defocus amounts and reliabilities based on the first signals and the second signals where the respective filtering processes have been performed, and a determiner (209) which determines a defocus amount used for focusing from among the plurality of defocus amounts based on a difference between the plurality of defocus amounts and at least one of the plurality of reliabilities.