Abstract: A photosensor system includes a housing in which are defined a primary passage, and a secondary passage intersecting the primary passage at substantially a right angle. A light source is disposed in the secondary passage to direct light toward the intersection of the passages, and a beam splitter plate is disposed at the intersection at about a 45.degree. angle with the primary passage to direct light from the light source toward one end of the primary passage. Disposed in that end of the primary passage is a lens for collimating the light rays and directing them outwardly of the housing. One side of the beam splitter plate contains a reflective finish or surface to reflect light impinging thereon, and the plate includes an aperture therein for allowing the passage of light. When light directed outwardly by the lens encounters a retroreflector, some of the light is reflected back through the lens and through the aperture in the beam splitter plate toward the other end of the primary passage.