Abstract: A particle sensing system in which light is concentrated at an inspection zone and deflected light is concentrated at a photosensor. A first reflecting surface is shaped to direct light toward the inspection zone, and a second reflecting surface is shaped to direct light deflected by particles in the inspection zone toward the photosensor. These two reflecting surfaces can be shaped so that an overwhelming part of the directions around the inspection zone are utilized for illuminating it and to direct light deflected toward the photosensor. A third reflecting surface, having spherical curvature with the center of curvature at the inspection zone permits utilization of an overwhelming part of the remaining directions around the inspection zone.