Abstract: An automatic microscope focusing system including a light source 44, a dual channel fiber optics bundle 56 and 58, chopper means 54 for alternately admitting light to the channels, a reticle 66 and associated optics to cast alternating images onto the surface of an inspected article W, return masks 82 and 88, and associated detectors 86 and 92 for inspecting the alternating reticle images, and control circuitry 36 and 38 responsive to the detector outputs and operative to drive the system microscope 10 into focus. The preferred embodiment also includes a flipping pupil 60 for accommodating particular microscope objectives.