An optical position sensing system includes a bezel surrounding a display, a position sensor assembly, and a processor for calculating touch locations. Prismatic film may be applied to the bezel. Each optical position sensor assembly includes a body. A lens holder holds an imaging window on a first side and a single element aspherical lens on a second side. The imaging window has an inside face shaped to form a shallow convex surface. The lens holder is mounted to a front face of the body such that the lens is aligned with an opening in the body. An optical sensor is mounted to a rear face of the body and aligned with the opening. A radiation source is positioned within the body above the lens holder and behind an illumination window. A light path separator is positioned between the illumination window and the imaging window.