An optical apparatus is disclosed which can reliably form AF images and split the AF images to provide excellent focus detection performance in the phase difference detection method. The optical apparatus comprises a light deflection unit including a deflection optical member. The deflection optical member deflects at least one of a first luminous flux and a second luminous flux relative to the other, the first and second luminous fluxes passing through a first area and a second area in the exit pupil of an optical system, respectively, and forming images on a photoelectrical conversion element. The light deflection unit comprises a light-limiting member which limits an image-forming area where at least one of the first and second luminous fluxes emerging from the light deflection unit forms the image on the photoelectrical conversion element.