High Quality Content by WIKIPEDIA articles! A reflector or reflex sight is a generally non-magnifying optical device that allows the user to look through a partially reflecting glass element and see an illuminated projection of an aiming point or some other image superimposed on the field of view. This is achieved by placing an image, a cross hair reticle or other pattern, at the focus of a lens and bouncing the image off a slanted glass plate, or at the focus of a partially reflecting curved mirror. The viewer looking through the glass plate or curved mirror reflector sees an image of the reticle in front of them that stays in alignment with the device the sight is attached to regardless of their eye position, removing most of the parallax error found in simple sighting devices.