A retroreflective sensor apparatus which includes a light source with a collimating lens and a photoelement with a condensing lens. The light source and the photoelement are positioned adjacent to and offset from each other. A mask is placed between the light source and the collimating lens on a side away from the photoelement to block a portion of the light from the light source from reaching the collimating lens. A method of constructing a retroreflective optical sensor including providing a light source with a collimating lens and a photoelement with a condensing lens. The light source and the photoelement are positioned adjacent to and offset from each other. An opaque mask is placed between the light source and the collimating lens on a side away from the photoelement to block a portion of the light from the light source from reaching the collimating lens. A reflector is positioned to receive light from the light source and reflect it to the photoelement. A retroreflective sensor apparatus in which a mask is placed between the photoelement and the condensing lens on a side away from the light source to block a portion of the light from the light source reflected by the reflector from reaching the photoelement. A method of constructing a retroreflective optical sensor in which a mask is placed between the photoelement and the condensing lens on a side away from the light source to block a portion of the light from the light source reflected by the reflector from reaching the photoelement.