An improved microlithographic imaging system (100) is disclosed. The system comprises a filter (183) substantially aligned with a first image plane, adjacent to an aperture (185). The filter is formed in response to an image projected by a light source (110) through a reticle (160) onto the first image plane. The improved microlithographic imaging system has higher resolution and depth of focus than prior art imaging systems, due to the additional filtering performed by the filter (183). A filter in accordance with the invention can be fabricated easily and inexpensively, using conventional microlithography techniques. A filter in accordance with the invention can also be used to detect or correct flaws in the reticle (160).