Optical instruments which establish an optical line or axis for the purpose of aiming a weapon. The axis includes the observer's eye, a suitable mark in the instrument, and the target. Most gunsights employ as their basis either a telescope or a partially reflective mirror. See also Mirror optics.
A typical rifle sight consists of a terrestrial telescopic system having an objective, an eyepiece, an erector lens, and a reticle. Sometimes a field lens is employed to ensure uniform illumination. Aircraft gunsights are usually of the reflector type (also known as reflex sights) and employ in their simplest form a lamp, a reticle, a collimating lens, and a glass plate or partially reflecting mirror (see illustration). The collimator images the reticle pattern at infinity, and the mirror superimposes this image over the target area. Artillery sights can assume various forms, the simplest of which is the collimator sight, consisting of an objective having a reticle at its focus. When the eye is so placed as to receive light simultaneously from the target and the reticle, the latter appears superimposedon the former and a line of sight is established. See also Lens (optics).
Reflex sight.
