1. An optical imaging system comprising: a mask that comprises multiple rotationally symmetrical regions; wherein the multiple rotationally symmetrical regions are shaped and positioned such as to define a modulation transfer function that is characterized by a substantially uniform response over a spatial frequency range wherein the substantially uniform response is substantially indifferent to an orientation of features of the object and to a location of the object within a deep depth-of-field region; wherein the modulation transfer function is above 5% over a normalized frequency range that ranges between zero and at least 1.3 for defocus parameter values that range between zero and 8; wherein a normalized frequency equals a spatial frequency divided by a diffraction limit of a perfectly aligned optical imaging system.