How do optical gun sights work

Sat 17th Sep, 2022

Optical sights are devices designed to assist accurate aiming with firearms. The general principle of operation of optical aiming devices is based on aligning a reticle or a sight with the intended target to ensure accurate hit. However, constructions and exact principles of each sight type vary.

Across the web and in the literature gun sights are often referred as military optical sights, combat optical sights or tactical optical sights, but these are just different names for the same thing. The actual types are listed below.

Let's see how optical gun sights work.


Combat optical sight types

Iron sight

Historically the first, iron sights use visual alignment of the target with the sight to form a line of sight. Technically, the iron sight consists of two: the front sight and the rear sight. During shooting, the shooter aligns the target, the front sight and the rear side to form one line. This ensures accurate hit. Well, as long as the weapon is accurate enough.

Reflex sights

Reflex sights or reflector sights use a special system based on a partially reflecting mirror to project the image of a reticle to the optical plane of the target. This allows the shooter to look through the sight optical system and see both the target and the reticle simultaneously.

There are two main types of reflex sights:

  1. Red dot reflex sights. This type of a gunsight consists of a light-emitting diode and a collimating mirror. The LED displays a red dot image that is focused at infinity and is partially reflected to the shooter's eye. As a result, the shooter sees a virtual red dot floating over the intended target.

  2. Holographic reflex sights or holosights. These optical sights use a 3D-hologram projected to the eye. Unlike red dot sights, holographic reticle is always in the same optical plane as the image of the target, hence the shooter does not need to refocus from the reticle to the target and back, and the aiming becomes easier.

Telescopic sights

Telescopic sights also known as rifle scopes or gun scopes are magnifying optical aiming devices intended to assist aiming at long range. The technical part includes a system of lenses.

The front end of the scope contains lenses that gather light reflected from the target. Normally, these objective lenses are designed to only allow certain types of light pass through. This is to reduce glares, and allow for maximum light to come in.

Then, the light comes to the central part of the scope where the optical image gets flipped back to its normal view with the correct side up.

Finally, the light goes through the lens on the second optical plane where the reticle image is added and comes out to the eye of the shooter from the near end of the scope.

Prism sights

Prismatic optical sights are technically very similar to telescope sights, but their optical system is simpler thanks to usage of special prisms instead of series of lenses. Such design has its pros and cons. Examples of prism sights are the best optical gun sights by Tijicon, including the most famous Trijicon ACOG® (Advanced Combat Optical Gunsight).

Prism sights are lighter and more compact than scopes, but have a significant disadvantage: the fixed eye relief. Unlike other types of sights, your eye must be on a certain specific distance from the sight. Otherwise, you just can't see the reticle and aim properly. Also, prism sights are somewhat more prone to parallax distortion.


How to choose sight optical system?

If you want to buy a sight optical device, make sure to pay attention to your purposes and conditions you will be using the optical sight at. Seeming disadvantages of an optical sight may turn out to be less important in your working conditions than you thought, while the hallmark features of another optical sight may only be important for certain uses.

If you are not sure what optical gun sight to prefer, ask a professional consultant like ones at to help you.



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