Calibration of pattern recognition in bright field imaging systems is disclosed. A target pattern on a substrate on the stage is brought into focus of a bright field system. The image is scanned in a first direction while measuring an edge scattering pattern from a feature of the target pattern. The edge scattering pattern is characterized by first and second peaks. A position of the bright field system's illuminator or beam shaping and relay optics is adjusted perpendicular to an optical path until the first and second peaks are approximately equal in height.
