What you need to know about reflex sights 

The basic technical principle of red dot sights is easy to explain: basically, a small LED creates a colored point of light that is reflected against a small, spherical, semi-transparent mirror and thrown back onto the front lens as a luminous target. Since the semi-transparent mirror only reflects a percentage of the light, it enables a correspondingly sharp view through the lens. The shooter can see both the target and the reflected point in one image line through the special mirror. Since the light beam of the point appears precisely from the direction of the sighting line, the point always appears in the right place, regardless of the position of the eye relative to the sighting device.

Nevertheless, you should know the point of impact of your weapon at different distances. Similar to a rifle scope, the point of impact can be corrected by adjusting the reticle. 

Many ask: Why is this point so razor-sharp? Very simple: Models with a straight front lens generate the luminous point using a laser, which is split into various small points using a prism and thus shaped into a point. However, many small points are required for this, which is why the illuminated point can sometimes appear blurred. In addition, the prism lens is expensive, so such devices also cost more money.

In other models with a beveled front lens, the point is generated by an LED and a semiconductor mirror. The shape of the (circular) point is already specified and can be represented much more sharply with the aid of the light-emitting diode. You don't need a prism (read: no expensive lens) for this, but one that is beveled and projects the point into the image plane. That is why these models are cheaper, but not less qualitative. To the contrary. 

The idea of a reflex sight was born in 1900. The telescope manufacturer, Howard Grubb, registered his invention for a patent (No. 12108), after which it was first used in the military (Air Force) in 1918. In the Second World War it was used in various artillery and anti-tank weapons. Unfortunately, there was a lack of small, powerful lighting elements, which is why passive light sources were needed. It wasn't until the mid-1970s that the Swedish company Aimpoint® achieved the decisive breakthrough: the developers were able to use the bundled light beam of an LED as a light source for the reflex sight. This technology also made it possible to build much smaller reflex sights and thus also made it possible to use them on handguns.

Reflex sights are - depending on the model - small, light and quite handy. They are ideal for quick sighting over short and medium distances, as both eyes can be open, and, depending on the distance (for example in combination with a magnifier), form a noticeably inexpensive alternative to classic rifle scopes.

As already mentioned above, the biggest advantage over a classic open sight is that it makes target acquisition easier: the rear sight, front sight and target no longer have to be brought into one optical axis; with the reflex sight only the luminous point and target have to match, and with reflex sights they lie in one plane. When using reflex sights with both eyes open, the so-called tunnel vision, which one is used to with telescopic sights, is eliminated and both spatial and peripheral vision are completely preserved. Thus target acquisition can be accelerated enormously by catching most, if not all, aiming errors such as tilting.

Before buying a reflex sight, every shooter should know what performance he or she expects for the given price. There are countless suppliers with an unmanageable number of models and features, so you should always think about what the sight should be able to do before buying. In general, it is always advisable to look at prices, equipment and (if possible) place of manufacture. Visier magazine writes the following:  

 „Models manufactured in Germany or in the USA already have a higher production cost. Japanese manufacturers, on the other hand, are professionals when it comes to the quality of optical lenses and electronics, and deliver both at comparatively lower costs.“

When making a purchase decision, the point size, point sharpness and point color should be important factors: point reticle only or switchable to circle/circle dot ? Do you prefer green reticle color or gold due to the weakness in red-green vision? You should ask yourself these questions beforehand. Most manufacturers indicate the size of their luminous dots in MOA (minute of angle, about 2,8 cm at 100 meters or 1 inch at 100 yards). For long guns and shooting distances of up to 150 meters, point sizes of <3 MOA are recommended, for short weapons <4MOA. 

It is also advisable to know the conditions in which you will operate, whether in extreme conditions, or with gloves; at the indoor range or in the wild. Do I need long battery life? Or transparent protective caps through which I can aim immediately even without opening them? As already described above, closed models or container constructions are suitable for extreme conditions. Models with solar cells and/or shake-awake function (automatic switch-on/switch-off) can save batteries and simple control buttons make use with gloves much easier. 

Another important question: is there a suitable assembly for my weapon? Before buying an optoelectronic sight, it should be clarified whether the manufacturer can supply a mount that corresponds to the weapon and its requirements, or whether a special format is required from the gunsmith. 

Determining the eye relief is only limited, if at all, by the mounting options on the weapon. When buying, always make sure that your new reflex sight restricts the field of view as little as possible, without neglecting lens protection. Depending on the application, open reflex sights with 24x32 mm lenses or tube reflex sights with a diameter of 20-30 mm are useful.