1. An optical system for imaging a scene, the optical system comprising: a first optical element, the first optical element being operative for forming a three-dimensional image field of the scene; and a plurality of microcameras that is arranged such that each microcamera has a unique optical axis that extends radially from the first optical element through the image field, each of the plurality of microcameras comprising (1) camera optics that includes at least one lens element and (2) a focal-plane array, and each of the plurality of camera optics being operative for relaying a different image region of the image field as an optical sub-image that is focused onto its respective focal-plane array, wherein at least one of the plurality of microcameras has controllable focus, and wherein at least one of the microcameras of the plurality thereof is operative for reducing the magnitude of an aberration in its relayed image region.