Image sensor and image pick-up apparatus

The invention provides an image sensor and an image pick-up apparatus. A plurality of pixels are arranged in the image sensor; each of the plurality of pixels has a plurality of photoelectric conversion units for receiving light beams having traversed different subpupillary regions of an imaging optical system, wherein an input pupil distance Zs of the image sensor meets the following conditions (shown in the description) with respect to a minimum output pupil distance Lmin of the optical imaging system and a maximum output pupil distance Lmax of the optical imaging system.