1. Apparatus for increasing depth of field and controlling focus related aberrations in a Phase Contrast Imaging system having an illumination source, illumination optics, and an illumination mask placed before a Phase Object to be imaged, and an objective mask and objective optics after the Phase Object to form an image at a detector, the improvement comprising: an optical Wavefront Coding mask having an aperture and placed between the Phase Object and the detector, said coding mask being constructed and arranged to alter the optical transfer function of the Phase Contrast Imaging system in such a way that the altered optical transfer function is substantially insensitive to the distance between the Phase Object and the objective optics over a greater range of object distances than was provided by the unaltered optical transfer function, wherein the coding mask affects the alteration to the optical transfer function substantially by affecting the phase of light transmitted by the mask; and a post processing element for processing the image captured by the detector by reversing the alteration of the optical transfer function accomplished by the coding mask.