sight

A sight or sighting device is any device used to assist in precise visual alignment (i.e. aiming) of ranged weapons, surveying instruments, aircraft equipment or optical illumination equipments with the intended target. Sights can be a simple set or system of physical markers that serve as visual references for directly aligning the user's line of sight with the target (such as iron sights on firearms), or optical instruments that provide an optically enhanced — often magnified — target image aligned in the same focus with an aiming point (e.g. telescopic, reflector and holographic sights). There are also sights that actively project an illuminated point of aim (a.k.a. "hot spot") onto the target itself so it can be observed by anyone with a direct view, such as laser sights and infrared illuminators on some night vision devices, as well as augmented or even virtual reality-enabled digital cameras ("smart scopes") with software algorithms that produce digitally enhanced target images. Simple sights At its simplest, a sight typically has two components, front and rear aiming pieces that have to be lined up. Sights such as this can be found on many types of devices including weapons, surveying and measuring instruments, and navigational tools. On weapons, these sights are usually formed by rugged metal parts, giving them the name "iron sights", as distinct from optical or computing sights. On many types of weapons they are built-in and may be fixed, adjustable, or marked for elevation, windage, target speed, etc. They are also classified in forms of notch (open sight) or aperture (closed sight). These types of sights can require considerable experience and skill, as the user has to hold proper eye position and simultaneously focus on the rear sight, the front sight, and a target, all at different distances, and align all three planes of focus.