Sep 03, 2020 | 10:03 pm 296 0

How a Red Dot Sight Works?

How a Red Dot Sight Works?

Many of those monitoring the market for automatic small arms are likely to have noticed the extensive discussion that has arisen around the use of new models. While, according to the developers, small size and high ballistic characteristics make the new models almost a dream and a top of perfection, professional shooters are mostly more restrained in their assessments. Without questioning the technical merits of the weapon samples submitted to their court, they note their extremely low efficiency when shooting at medium and long distances.

The matter is that the overwhelming majority of novelties by tradition are equipped with a standard sight in the form of a front and rear iron sight, which due to the short length of the barrel appear too close to the shooter's eye and do not allow to aim quickly and accurately. Attempts to solve the problem by equipping the weapon with a magnified sight or laser designator, also failed. It was found out that due to its small field of view and low aperture ratio, the telescopic sight is effective only when shooting at long distances at low-moving and well lit targets. However, it is almost impossible to quickly hit a moving target at medium or short range, as well as to fire the sight on the move, i.e. in the most typical conditions of semiautomatic weapon use.

Obviously, for the high ballistic characteristics of the small-size automatic weapon to become a real advantage, it should be equipped with a sight with a wide field of view, which does not require eye-shot recalibration when aiming. And for effective shooting, the sighting measure of such a sight should be instantly identified and be clearly visible at any illumination level. In this case it is desirable that the sighting is not influenced by the mixing of the eye with the axis of the sight.

All these requirements are mosly satisfied by so-called red dot sights.

What is a Red Dot Optic?

Optical circuitry of most red dot sights consists of small-sized light source and optical systems, which directs light source radiation only towards the exit pupil of the sights. Typically, it transmits the image without magnification, converting the light source radiation so that the shooter can simultaneously see a clear image of the far field of view and the sighting mark in the form of a small light spot when observing through the sight. The mixing of the arrow's eye within the scope's exit pupil does not affect the visible position of the reticle on the remote target. In this way, the shooter can avoid fixing his eyes on the axis of the gun barrel and effectively look through the optic towards the target in the distance. In order to be able to aim accurately, the shooter simply points a light spot on the target of the reticle.

The colour and visible size of the sighting mark are important. The preference for its bright red colour is due to the fact that there are practically no red objects in nature. Therefore such a mark is contrasted on the general background of objects. Besides, red is psychologically perceived as a color of danger and attention is fixed on it first of all. As for the visible size of the reticle, its optimal size depends on the type of weapon. If for a long rifled weapon, designed for shooting at a distance of more than 150 meters, the size of the reticle is desirable to have close to the maximum resolution of the eye, then for a hunting smoothbore and short-barrelled automatic weapon is more preferable reticle with the visible size of about 10 Minutes of angle, which corresponds to the resolution of the eye in low light conditions and is about half the size of the iron site of the M-16 semi-automatic rifle.

How Do They Work?

In simple and cheap models of red dot sights the optical system is usually made in the form of transparent spherical meniscus, on the concave surface of which there is a mirror coating reflecting red light. Normal red LED is used as a light source. Mutual position of the meniscus and the light source is chosen so that the aiming axis coincided with the axis of the light beam reflected from the meniscus, and the light source was in the focal plane of the meniscus and did not fall into the line of sight. The shooter observed the target through the transparent meniscus. The LED light reflected by the meniscus hits the shooter's eyes formed on the target and he sees at the same time a clear image of the light spot, which indicates the point of aim.

Due to the misalignment of the optical axes of the meniscus, the light source and the reticle, this system provides a relatively small field of view in which the visible position of the reticle exactly matches the aiming point. The open design of the sight does not protect the optics and light source from moisture and dirt. The absence of a protective cover leads to strong glare of the meniscus in conditions of lateral sunlight, which negatively affects shooting results.

More expensive models use a lens optic system and a narrow strip spotlight LED with increased light output. The radiation generated by the optical system is generated in the field of view of the sight by means of a spectral-selective mirror. Therefore the field of view of such a sight is larger. To protect the optical system from moisture and dirt the housing of most models is sealed with protective glass. In addition, the reticle is usually equipped with a smooth or step-by-step brightness control of the reticle.

New in the red dot sights class is an optical system on holographic principles. Due to this the sight became lighter and smaller, its angle of view increased more than three times, and light losses and power consumption decreased almost twice. MOA hits on targets when using the red dot scope is markedly reduced and possibly tends to 1.

Different Types of Red Dots

• Open sights. The small size of these sights makes it an ideal choice, for example, for air and fire pistols and not only for them. Open sights with red dot are often used on shotguns, especially when operation of the weapon does not require harsh weather conditions, such as prolonged frost, or long continuous rain. These sights are also mounted on crossbows and bows. The open type also includes holographic sights, the main advantage of which is minimization of distortion of the sights type in relation to the aiming object, and their compact size is often the decisive argument when choosing between closed type and holographic sights.

• Closed sights. These are sights in which the light source creating the reticle is located in a closed (sealed) housing, equipped with lenses on both sides, as opposed to open sights, where only one lens is available. Obviously, the main advantage of closed sights is their resistance to adverse weather conditions, and they lose out to open sights in general view. Another advantage of closed sights is that they are protected from mechanical influences, so it is this type of sight that is chosen by arrows who have to sneak out in search of game, for example, through dense forest thickets. If an analogy is drawn with a copperhead that uses a semi-active laser guidance system that illuminates the target from the ground or on board, using a red dot in the sight would significantly reduce accuracy losses.

How to Shoot with a Red Dot Sight

The aiming process can be described as follows:

• The lens (lens system) of this type of sight projects the aiming mark to infinity.

• Radiation from the light source (target) becomes visible to the eye of the arrow (observer) due to a parallel flow.

• When the focus of the shooter's eye shifts in transverse directions, the reticle is moved along a switch lens, concentrating on the target regardless of the position of the shooter's eye relative to the reticle itself.

• The arrowhead pupil does not have to be on the reticle axis and, thanks to the above mentioned properties of the collimator sight, it suffices to be within the projection of the lens.

In the case of a crossfire, the red dot sights may not be as effective, but this does not diminish their advantages in terms of speed and accuracy.


Manual small arms are mainly equipped with one of two standard type of rails:

• Weaver-rail (21 mm wide);

• Dove-tail (width 8-12 mm).

The Picatinny rail, developed as part of the U.S. military standard, is also considered a Weaver-type, as any device with the Picatinny rail mount will easily become a Weaver-type. Accordingly, any of the mass-produced sights will have a weaver-type or dove-tail mount (or will be supplied without a bracket at all). But some models of sights are equipped with special double-sided bracket. They can be mounted on any type of slats and used on any weapon.

Due to small body length red dot sights are often equipped with monoblock brackets, while optical sights are often installed on separate mounting rings. Naturally, the one-piece bracket provides more rigid grip on the bar and greater recoil resistance.

If you plan to use this type of sight with something more serious than LPG, choose a mount made of strong metal alloy - steel or aircraft aluminum. It is also desirable that in addition to tie-in/clamping screws, the sight mount has 2-3 locking pins, which will be clamped in slits of the bar when installed.

• Low-fitting sights practically do not change the natural line of sighting: they are preferred by those for whom accuracy is most important.

• High-mounted sights are also used to see the home sight of a weapon in the formed "window".

• Red dot quick-detachable sights are usually fitted with a flag-type clip. In case of unexpected device failure, this design will allow the bracket to detach in a few seconds and continue firing using the standard "mechanics".


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