1. An image input apparatus comprising: an imaging optical system; a microlens array having a plurality of microlenses two-dimensionally arrayed with a predetermined pitch in a vicinity of a focal plane of the imaging optical system; and a photoreceptor array having a plurality of photoreceptors for each of the microlenses, each of the photoreceptors receiving bundles of rays passing through one of different regions at an exit-pupil of the imaging optical system, wherein a power of the microlens and a gap between the microlens array and the photoreceptor array are determined so that a cross-sectional dimension of the bundles of rays for forming an image of each of the photoreceptors related to the microlens is equal to or smaller than the pitch of the microlens, within a range from the microlens array to a predetermined distance.