Abstract: A method for measuring an optical performance of a projection optical system in an exposure apparatus that exposes a pattern on a reticle onto a substrate includes the steps of determining an pupil area in the projection optical system, scanning a test reticle or a reference plate, imaging a test pattern on the test reticle or the reference plate onto a surface of the substrate via the pupil area in the projection optical system which has been determined by the determining step, and measuring a positional offset between a predetermined position and an image of the test pattern that has been imaged by the imaging step.