1. A microlithography system comprising: illumination means for projecting a sharp image of a subresolution aperture onto an alignment target; means for scanning said alignment target through said sharp image at a plurality of scan positions; means for blocking collection of light directly reflected from said alignment target; collection means for collecting light scattered from the vicinity of said alignment target at each said scan position; and detection means for integrating and filtering said collected light, said integrated collected light being filtered to provide an alignment signal pulse at an edge of an alignment pattern.