An approach to spatial frequency filtering is described where 'zero order' mask diffraction information is reduced, enhancing imaging performance. This method of resolution enhancement is accomplished by filtering in an alternative pupil plane of the objective lens, specifically near or beyond the mask pellicle plane. By introducing an angular specific transmission filter into the Fraunhofer diffraction field of the mask, user accessibility is introduced, allowing for a practical approach to frequency filtering. This is accomplished using a specifically designed interference filter coated over a transparent substrate. Analysis of the approach is given along with result from experiments for contact features using a full field high NA 148nm exposure tool.