Abstract: A system for automatically detecting dust or other minute particles on a large-area, optically unpolished surface such as a face of a glass reticle plate used in the production of microelectronic circuits. The system irradiates the surface with a narrow, high intensity beam of monochromatic radiation at a grazing angle, typically 1/2 degree with respect to the surface. An oscillating mirror scans the beam across the moving surface in a direction generally perpendicular to the direction of plate advance. A beam splitter provides separate inspecting beams for each surface of the plate. Optical systems characterized by a high numerical aperture are positioned on opposite sides of the plate to collect radiation which is scattered from the particles. The optical systems are oriented to accept scattered radiation, and typically have their optical axes at an angle in the range of 60.degree. to 160.degree. measured from the direction of advance.