An optical sensor for imaging an input object, such as a fingerprint, on a sensing region of a display is disclosed. The sensor includes a transparent substrate having a first side and a second side opposite the first side. An array of detector elements is positioned above the first side of the transparent substrate and an angle limiting reflector is positioned below the second side of the transparent substrate. The angle limiting reflector is configured to reflect light incident on the angle limiting reflector within a limited acceptance angle towards the array detector elements.