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A red dot sight is a common classification for a type of non- magnifying reflector (or reflex) sight for
firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...
s, and other devices that require aiming, that gives the user a point of aim in the form of an illuminated red dot. A standard design uses a red
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
(LED) at the focus of collimating optics which generates a dot-style illuminated
reticle A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscop ...
that stays in alignment with the weapon the sight is attached to, regardless of eye position (nearly
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...
free). They are considered to be fast-acquisition and easy-to-use gun sights for civilian target shooting, hunting, or in police and military applications. Aside from firearm applications, they are also used on cameras and telescopes. On cameras they are used to photograph flying aircraft, birds in flight, and other distant, quickly moving subjects. Telescopes have a narrow field of view and therefore are often equipped with a secondary "finder scope" such as a red dot sight.


Description

The typical configuration for a red dot sight is a tilted spherical mirror reflector with a red
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
(LED) at its off axis focus. The mirror has a partially silvered multilayer dielectric dichroic coating designed to reflect just the red spectrum allowing most other light to pass through it. The LED used is usually deep red 670
nanometre 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
wavelength since they are very bright, are high contrast against a green scene, and work well with a dichroic coating since they are near one end of the
visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to ...
. The size of the dot generated by the LED is controlled by an aperture hole in front of it made from metal or coated glass. The 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 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. Using a "dot" shaped reticle also greatly simplifies the sight since the small diameter image does not require a sophisticated optical reflector to focus it. More complex reticle patterns such as crosshairs or concentric circles can be used but need more complex aberration free optics. Like other reflector sights, the
collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...
image of the red dot is truly
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...
free only at infinity, with an error circle equal to the diameter of the collimating optics for any target at a finite distance. This is compensated for by keeping the dot in the middle of the optical window (sighting down the sight's
optical axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light pro ...
). Some manufacturers modify the focus of the LED/optical collimator combination, making models with the optical collimator set to focus the dot at a finite distance. These have a maximum amount of parallax due to eye movement, equal to the size of the optical window, at close range, diminishing to a minimal amount at the set distance (somewhere around a desired target range of 25–50 yards). Sights may also use a more sophisticated optical system that compensates for off axis
spherical aberration In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. Lenses and curved mirrors are prime examples, because this shape is easier to manufacture. Light rays that strik ...
, an error that can cause the dot position to diverge off the sight's
optical axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light pro ...
with change in eye position. The optics used is a type of
Mangin mirror In optics, a Mangin mirror is a negative meniscus lens with the reflective surface on the rear side of the glass forming a curved mirror that reflects light without spherical aberration if certain conditions are met. This reflector was invented i ...
system, consisting of a meniscus lens corrector element combined with the semi-reflective mirror, sometimes referred to in advertising as a "two lens" or "double lens" system. Although these are referred to as "parallax free" sights, the system keeps the aiming dot in alignment only with the sight itself and does not compensate the inherent parallax errors induced by a collimated sight. Red dot sights generally fall into two categories, "tube" or "open" designs. "Tube sights" look similar to a standard
telescopic sight A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a '' reticle'' – mounted in a focally appropriate ...
, with a cylindrical tube containing the optics. Tube sights offer the option of fitted dust covers and the ability to add filters, such as polarizing or haze filters, and glare reducing sunshades. Since a reflector sight really needs only a single optical surface, the "reflector", the tube is not needed. This allows for non-tubed "open sights" that consist of a flat base, with a single loop of material to support the reflective optics. Most red dot sights have either active or passive adjustments for the dot brightness, allowing a very bright dot for high visibility in bright conditions, and a very dim dot to prevent loss of
night vision Night vision is the ability to see in low-light conditions, either naturally with scotopic vision or through a night-vision device. Night vision requires both sufficient spectral range and sufficient intensity range. Humans have poor night v ...
in low light conditions.


History

The idea of attaching a reflector (or ''reflex'') sight to a firearm has been around since the sight's invention in 1900. Many different types of reflector sights specifically designed for firearms have been marketed, some lit by batteries and some lit by ambient light. The Weaver Qwik-Point presented the viewer with a red aiming dot generated by a red plastic "
light pipe Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 ...
" used to collect ambient light. All had the reticle illumination drawback common with reflector sights small enough for a firearm: proper ambient lighting could not be depended on and
incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxi ...
s could drain a battery in a few hours. In 1975, the Swedish optics company Aimpoint AB marketed the first "electronic" red dot sight combining a reflecting curved mirror and a light-emitting diode, based on a design by
Helsingborg Helsingborg (, , , ) is a city and the seat of Helsingborg Municipality, Scania (Skåne), Sweden. It is the second-largest city in Scania (after Malmö) and ninth-largest in Sweden, with a population of 113,816 (2020). Helsingborg is the cent ...
engineer
John Arne Ingemund Ekstrand John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...
. The sight was called the "Aimpoint Electronic" and had a closed tube design that could be mounted similar to a telescopic sight. The LED could run for 1500 to 3000 hours on mercury batteries. Other manufacturers soon followed with over a dozen offering models today. Newer generation red dot sights were produced with lower power consumption LEDs and power saving electronics, allowing them to run for years without being turned off. In 2000, the U.S. military introduced a red dot sight into field use, the Aimpoint CompM2, designated the "M68 Close Combat Optic".


Reticle sizes

Red dot sight
reticle A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscop ...
sizes are measured in
milliradian A milliradian ( SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting t ...
s (mrad) and minutes of angle (MOA), which both are angular measurements, making them handy units to use in
ballistics Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing a ...
. Milliradians are handy when using
SI units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...
for range and subtensions, and can be calculated by measuring the group size in millimeters (or in centimeters and multiplying by a factor of 10) and dividing by the range measured in meters. Minutes is another convenient measure for shooters using English units, since 1 MOA approximately subtends 1.0472 inches at a distance of 100 yards (91.44 m), which is generally rounded to 1 inch at 100 yards. While MOA sights have traditionally been popular in the U.S., scope sights with mrad adjustments and reticles are now also becoming increasingly popular in the U.S. The most common reticles used today in red dot sights both for handguns and rifles are small dots covering between 0.6 and 1.6 mrad (2 to 5 MOA). The choice of red dot reticle size depends on the user needs. A larger and brighter red dot makes for faster target acquisition, but may obscure the target and thereby inhibit precise aiming, while a smaller and dim dot allows for more precise but slower aiming. The 1.6 mrad (5 MOA) dot is small enough not to obscure most handgun targets, and large enough for most competition shooters to quickly acquire a proper sight picture. Red dots for rifles typically have a smaller dot, often 0.6 to 0.8 mrad (2 to 3 MOA). When red dot sights started to appear at the
practical shooting Practical shooting, also known as dynamic shooting or action shooting, is a set of shooting sports where the competitors try to unite the three principles of precision, power, and speed, by using a firearm of a certain minimum power factor to sc ...
competition circuit in the 1990s, reticle sizes of up to 3, 4.5 or even 6 mrad (10, 15 or 20 MOA) were common in order to compensate for the lack of bright illumination. However, as red dot technology and production quality has advanced, the market trend in all types of sport shooting has gone towards the smaller dots used today.


Mounting types

There are various mounting types (also called "footprints") for red dot sights:Footprints/Mounting Standards on Red Dot Sights - Optics info
/ref> ;Docter/Noblex standard: The mounting pattern used by the largest number of manufacturers, perhaps due to the wide range of aftermarket mounts available. The mounting standard uses two screws and four notches acting as recoil lugs. Used on red dot sights such as Docter/Noblex sights, Burris Fastfire, Vortex Viper, Leica Tempus, etc. ;C-More standard: A mounting standard introduced by C-More Sights. Uses two screws and two notches acting as recoil lugs. Used on red dot sights such as Delta Optical MiniDot, Kahles Helia, Vortex Razor and Sig Sauer Romeo3. ;Shield standard: A proprietary standard used by Shield Sights. Similar in shape to the Noblex/Docter footprint, but with other dimensions. In addition to the Shield red dot sights, it is also used on the Leupold Delta Point Pro. ;Trijicon RMR standard: Has two screw holes, and two shallow notches acting as recoil lugs. Mainly used on the Trijicon RMR red dot sight, as well as on some Holosun sights. ;Aimpoint Micro standard: First introduced on the small tube sight variants of Aimpoint, but today used by other manufacturers as well. The mounting standard uses four screws and one cross slot acting as a recoil lug. Used on red dot sights such as Aimpoint Micro, Vortex Crossfire, Sig Sauer Romeo 4 & 5, and some Holosun Paralow variants. ;Other unique footprints: Some notable red dot sights which have unique footprints not compatible with any of the above are Sig Sauer Romeo 1, Steiner MRS, Holosun Paralow 403A and Aimpoint ACRO.


Uses

Red dot sights place the target and the reticle on nearly the same optical plane, allowing a single point of focus. This makes them fast-acquisition and easy-to-use sights, allowing the user to keep their attention on the field of view in front of them. They are common in speed shooting sports such as IPSC. Military units and police forces have also adopted them. Red dot sights are also popular among
paintball Paintball is a competitive team shooting sport in which players eliminate opponents from play by hitting them with spherical dye-filled gelatin capsules called paintballs that break upon impact. Paintballs are usually shot using low-energy a ...
and
airsoft Airsoft is a team game in which participants eliminate opposing players by tagging them out of play with spherical plastic projectiles shot with mock air weapons(usually powered by an electronic motor) called airsoft guns. Although similar ...
players for similar reasons. Because there is no magnification, the shooter need not worry about parallax or eye relief. The long eye relief makes red dot sights appropriate for firearms with heavy
recoil Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, as according to Newton's third law the force r ...
that might drive a conventional short eye relief telescopic sight into the shooter's eye. Since dot sights can be mounted at any distance from the shooter's eye with no issues of focus, military rifle mounts usually place the sight in any mechanically-convenient mounting position, such as the carrying handle of the
M16 rifle The M16 rifle (officially designated Rifle, Caliber 5.56 mm, M16) is a family of military rifles adapted from the ArmaLite AR-15 rifle for the United States military. The original M16 rifle was a 5.56×45mm automatic rifle with a 20-r ...
, or on a rail system (typically a
Picatinny rail The Picatinny rail ( or ), or Pic rail for short, also known as a MIL-STD-1913 rail, 1913 rail or STANAG 2324 rail (cancelled), is a military standard rail interface system that provides a mounting platform for firearm accessories. It was ...
) on top of the rifle. This leaves plenty of room for night vision equipment to be used with the red dot sight. Miniature red dot sights are becoming increasingly popular for use on pistols, both for competition and military applications.The Beginner's Guide to Pistol Reddots
/ref> A red dot sights can be combined with a
red dot magnifier A red dot magnifier is an optical telescope that can be paired with a non-magnifying optical sight on a weapon to create a telescopic sight. They work with the parallel collimated reticle image produced by certain non-magnifying sights so, con ...
, a small
optical telescope An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through elect ...
mounted behind the sight to provide increased magnification to a shooter's view.


Further reading

* * * *


See also

* Aimpoint CompM2, CompM4, and
ITL MARS The ITL MARS (Multi-purpose Aiming Reflex Sight) is a gun sight that combines two sighting devices, a reflex sight and a laser sight, as well as a backup iron sight. It is designed and produced by ITL Optronics company, based in Israel. The ...
red dot sights * Collimator sight, blind non-magnifying sights that (depending on the reticle used) had a "red dot" aiming point * Glossary of firearms terminology *
Iron sight Iron sights are a system of physical alignment markers (usually made of metallic material) used as a sighting device to assist the accurate aiming of ranged weapons (such as a firearm, airgun, crossbow or even compound bow), or less commonly ...
*
Holographic weapon sight A holographic weapon sight or holographic diffraction sight is a non- magnifying gunsight that allows the user to look through a glass optical window and see a holographic reticle image superimposed at a distance on the field of view. The holog ...
*
Laser sight A laser sight is a device attached or integral to a firearm to aid target acquisition. Unlike optical and iron sights where the user looks through the device to aim at the target, laser sights project a beam onto the target, providing a visua ...
, projects a red (or other-colored) aiming point onto a distant target *
Telescopic sight A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a '' reticle'' – mounted in a focally appropriate ...
* Prism sight, a type of telescopic sight


References

{{Firearms Firearm sights