Product Code Database
A reflector sight or reflex sight is an Optics sight that allows the user to look through a partially reflecting glass element and see an aiming point or some image (helping to aim the device, to which the sight is attached, on the target) superimposed on the field of view. These sights work on the simple optical principle that anything (such as an illuminated reticle) at the focus of a lens or curved mirror will appear to be sitting in front of the viewer at infinity. Reflector sights employ some form of "reflector" to allow the viewer to see the infinity image and the field of view at the same time, either by bouncing the image created by lens off a slanted glass plate, or by using a mostly clear curved glass reflector that images the reticle while the viewer looks through the reflector. Since the reticle image is at infinity, it stays in alignment with the device to which the sight is attached regardless of the viewer's eye position to the sight, removing most of the parallax and other sighting errors found in simple sighting devices.
Since their invention in 1900, reflector sights have come to be used as gun sights on various weapons. They were used on fighter aircraft, in a limited capacity in World War I, widely used in World War II, and still used as the base component in many types of modern . They have been used in other types of (usually large) weapons as well, such as anti-aircraft gun sights, anti-tank gun sights, and any other role where the operator had to engage fast moving targets over a wide field of view, and the sight itself could be supplied with sufficient electrical power to function. There was some limited use of the sight on after World War II, but the sight came into widespread use during the late 1970s with the invention of the red dot sight. This sight uses a red light-emitting diode (LED) as its illumination source, making a durable, dependable sight with an extremely long illumination run time.
Other applications of reflector sights include sights on surveying equipment, optical telescope pointing aids, and camera .
A common type (used in applications such as aircraft gun sights) uses a collimating lens and a beam splitter. This type tends to be bulky since it requires at least two optical components, the lens and the beam splitter/glass plate. The reticle collimation optics are situated at 90° to the optical path making lighting difficult, usually needing additional electric illumination, condensing lenses, etc. A more compact type replaces the lens/beam splitter configuration with a half silvered or dichroic filter curved collimating mirror set at an angle that performs both tasks of focusing and combining the image of an offset reticle. This type is most often seen as the red dot type used on small arms. It is also possible to place the reticle between the viewer and the curved mirror at the mirror's focus. The reticle itself is too close to the eye to be in focus but the curved mirror presents the viewer with an image of the reticle at infinity. This type was invented by Dutch optical engineer Lieuwe van Albada in 1932, originally as a camera viewfinder, and was also used as a gunsight on World War II : the US M9 and M9A1 "Bazooka" featured the D7161556 folding " Reflecting Sight Assembly".
The viewing portion of a reflector sight does not use any refraction optical elements, it is simply a projected reticle bounced off a beam splitter or curved mirror right into the users eye. This gives it the defining characteristics of not needing considerable experience and skill to use, as opposed to simple mechanical sights such as iron sights. A reflector sight also does not have the field of view and eye relief problems of sights based on optical telescopes: depending on design constraints their field of view is the user's naked eye field of view, and their non-focusing collimated nature means they do not have the optical telescopes constraint of eye relief. Reflector sights can be combined with telescopes, usually by placing the telescope directly behind the sight so it can view the projected reticle creating a telescopic sight, but this re-introduces the problems of narrow field of view and limited eye relief. The primary drawback of reflector sight is that they need some way to illuminate the reticle to function. Reticles illuminated by ambient light are hard to use in low light situations, and sights with electrical illumination stop functioning altogether if that system fails.American rifleman: Volume 93, National Rifle Association of America - THE REFLECTOR SIGHT By JOHN B. BUTLER, page 29
It was noted soon after its invention that the sight could be a good alternative to iron sights and also had uses in surveying and measuring equipment. The reflector sight was first used on German fighter aircraft in 1918British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke, page 134 and widely adopted on all kinds of fighter and bomber aircraft in the 1930s. By World War II the reflector sight was being used on many types of weapons besides aircraft, including anti-aircraft guns, naval guns, anti-tank weapons, and many other weapons where the user needed the simplicity and quick target acquisition nature of the sight. Through its development in the 1930s and into World War II the sight was also being referred to in some applications by the abbreviation " reflex sight".Applied physics Chauncey Guy Suits, George Russell Harrison, Louis Jordan - 1948, page 222 - "One of the most important types of gun sights used by the Army and Navy during the war was the reflex, or reflector, sight."
Since the collimated light image produced by the sight is only truly parallax free at infinity, the sight has an error circle equal to the diameter of the collimating optics for any target at a finite distance. Depending on the eye position behind the sight and the closeness of the target this induces some aiming error. For larger targets at a distance (given the non-magnifying, quick target acquisitions nature of the sight) this aiming error is considered trivial. On small arms aimed at close targets this is compensated for by keeping the reticle in the middle of the optical window (sighting down its optical axis). Some manufacturers of small arms sights also make models with the optical collimator set at a finite distance. This gives the sight parallax due to eye movement the size of the optical window at close range which diminishes to a minimal size at the set distance (somewhere around a desired target range of ).
Compared to standard telescopic sights, a reflector sight can be held at any distance from the eye (does not require a designed eye relief), and at almost any angle, without distorting the image of the target or reticle. They are often used with both eyes open (the brain will tend to automatically superimpose the illuminated reticle image coming from the dominant eye onto the other eye's unobstructed view), giving the shooter normal depth perception and full field of view. Since reflector sights are not dependent on eye relief, they can theoretically be placed in any mechanically-convenient mounting position on a weapon.
Reflector sights as aircraft gun-sights have many advantages. The pilot/gunner need not position their head to align the sight line precisely as they did in two-point mechanical sights, head position is only limited to that determined by the optics in the collimator, mostly by the diameter of the collimator lens. The sight does not interfere with the overall view, particularly when the collimator light is turned off. Both eyes may be used simultaneously for sighting.
The optical nature of the reflector sight meant it was possible to feed other information into field of view, such as modifications of the aiming point due to deflection determined by input from a gyroscope.Lon O. Nordeen, Air warfare in the missile age, page 265 1939 saw the development by the British of the first of these , reflector sights adjusted by gyroscope for the aircraft's speed and rate of turn, enabling the display of a lead-adjusted sighting reticle that lagged the actual "boresight" of the weapon(s), allowing the boresight to lead the target in a turn by the proper amount for an effective strike
As reflector sight designs advanced after World War II, giving the pilot more and more information, they eventually evolved into the head-up display (HUD). The illuminated reticle was eventually replaced by a video screen at the focus of the collimating optics that not only gave a sighting point and information from a lead-finding computer and radar, but also various aircraft indicators (such as an artificial horizon, compass, altitude and airspeed indicators), facilitating the visual tracking of targets or the transition from instrument to visual methods during landings.
The mid- to late 1970s saw the introduction of what are usually referred to as red dot sights, a type that gives the user a simple bright red dot as an aiming point. Invention intelligence: Volume 11, Inventions Promotion Board, National Research Development Corporation of India, 1976, page 12 The typical configuration for this sight is a compact curved mirror reflector design with a red light-emitting diode (LED) at its focus. Using an LED as a reticle is an innovation that greatly improves the reliability and general usefulness of the sight: there is no need for other optical elements to focus light behind a reticle; the mirror can use a dichroic filter coating to reflect just the red spectrum, passing through most other light; and the LED itself is solid state and consumes very little power, allowing battery-powered sights to run for hundreds and even tens of thousands of hours.
Reflector sights for military firearms (usually referred to as reflex sights) took a long time to be adopted. The US House Committee on Armed Services noted as far back as 1975 on the suitability of the use of reflex sight for the M16 rifle,"Hearings before and special reports made by Committee on Armed Services of the House of Representatives on subjects affecting the naval and military establishments", Volume 980 - Page 3002 United States. Congress. House. Committee on Armed Services - Political Science, 1975 but the US military did not widely introduce reflector sights until the early 2000s with the Aimpoint CompM2 red dot sight, designated the "M68 Close Combat Optic".
Sights that use dot reticles are almost invariably measured in minutes of arc, sometimes called "minutes of angle" or "moa". Moa is a convenient measure for shooters using Imperial or US customary units, since 1 moa subtended angle approximately at a distance of , which makes moa a convenient unit to use in ballistics calculations. A 5 moa (1.5 milliradian) dot is small enough not to obscure most targets, and large enough to quickly acquire a proper "sight picture". For many types of action shooting, a larger dot has traditionally been preferred; 7, 10, 15 or even 20 moa (2, 3, 4.5 or 6 mil) have been used; often these will be combined with horizontal and/or vertical lines to provide a level reference.
Most sights have either active or passive adjustments for the reticle brightness, which help the shooter adapt to different lighting conditions. A very dim reticle will help prevent loss of night vision in low-light conditions, while a brighter reticle will display more clearly in full sunlight.
Modern optical reflector sights designed for firearms and other uses fall into two housing-configurations: "tubed" and "open".
These sights are also used on astronomical as , to help aim the telescope at the desired object. There are many commercial models, the first of which was the Telrad, invented by amateur astronomer Steve Kufeld in the late 1970s. Others are now available from companies such as Apogee, Celestron, Photon, Rigel, and Televue.
Reflector sights are also used in the entertainment industry in productions such as live theater on Follow spot. Sights such as Telrad's adapted for use and the purpose built Spot DotLighting dimensions, Volume 19, Page 114, Lighting Dimensions Associates, 1995 allow the spotlight operator to aim the light without turning it on.
|
|
