1. An imaging system for three dimensional localization, imaging, and/or tracking of an object, the imaging system comprising: an optical system comprising an objective lens, wherein the optical system produces a spatially varying phase difference imposed among different components of the light coming through different parts of the objective lens to generate a three dimensional point spread function image, wherein a maximum of the point spread function describes a curve in three-dimensional space; at least one sensor array configured to receive one or more images of an object through the optical system; and a processing module configured to provide one or more of the following functions imaging of the object, axial ranging of the object, a three dimensional estimate of a position of the object, and tracking of the object.