1. An optical system comprising: an imaging system that generates a point spread function by control of one or more associated pupil functions of the optical system, the point spread function having a transverse profile that retains its fundamental shape with axial propagation and remains offset from an axis; a sensor array configured to receive light from at least one object through the imaging system and provide one or more images of the object; and a processing device configured to: recover a representation of the one or more associated pupil functions of the imaging system using a phase retrieval algorithm; determine the position of two concentrations of recorded light in the one or more images that are point spread function representations of the object imaged through the imaging system; and localize the object in three dimensions based at least in part on a transverse shift of the two concentrations of recorded light in at least one of the one or more images of the object.