Mini Red Dot Sight

In a modern reflex red dot sight, a battery is used to power a single LED. This LED projects either a red or green light onto a concave lens. Thanks to a special coating, that illuminated point becomes visible to your eye. Because the dot only appears on one plane, there is no sight alignment required. It’s really that simple.

Holographic sights take this technology a step further by directing a laser along a series of mirrors inside the optic. As a result, the reticle remains unchanged by external magnifiers and doesn’t suffer from parallax distortion. In fact, holographic red dot sights will continue to function accurately even if the lens is partially broken or obscured. As long as some glass is present and visible, the reticle will appear and continue to work properly.

One disadvantage of red dot sights is the parallax effect we mentioned earlier. This kind of distortion happens when the reticle moves in relation to the shooter’s head. Parallax distortion is most common at very close ranges (usually less than 25 yards), so practical accuracy doesn’t suffer too much. The amount of parallax distortion differs between makes and models, as well.

Another limitation of traditional reflex-type red dot sights is the fact that the reticle increases in size when paired with a magnifier. That means that a three-MOA dot, which appears to be three inches in diameter when placed on a target at 100 yards, will appear to be nine inches in diameter on the same target when paired with a three-power magnifier. This makes it harder to see and accurately engage your target.

As I mentioned in the introduction, there are several types of red dot sights, each using a different principle to make the sight function. There are three main types of pistol red dots:

Reflex
Reflex sights work by emitting a beam via an LED, which is then bounced off of a translucent mirror inside of the optic. That laser is bounced back from the angled mirror into your eye. So, when you look through the scope, you see through the translucent mirror as well as seeing the bounced laser, and the effect is the perception of a dot or other reticle over the target.

Since all of the technologies involved in a reflex sight are fairly simple, these are often the most affordable kinds of red dot sights, ranging from as little as $20 to over $500.

Prismatic
Prismatic sights, as you can probably guess by the name, make use of a prism. In particular, prismatic sights have their reticles etched into a lens, and then the image of the target is focused using a series of prisms that the user can adjust for sharpness, and, often, magnification.

Prismatic sights well predate red dots, though red dot prismatic sights take the above concept and use a battery to illuminate the reticle. The major benefit here is that since the reticle is etched on the lens, it is super sharp and, usually, can function reasonably well even without a battery installed, albeit not as a true red dot. These sights generally cost anywhere from $120 to $500.

Holographic
AGM Global, a manufacturer of high-end sights, explains in detail how holographic sights work.

Holographic sights use a laser, a series of reflectors, and a grate with an image on it to project an image on an output display. In gun sights, this grate usually has a two-dimensional reticle, though a hologram can, technically, be three-dimensional as well.

In making the output screen a transparent piece of glass, the result is a reflection of an optic being placed in the middle of a conveniently clear window for the shooter. These sights have no parallax, or shift in perceived point of impact, making them highly accurate, but the complexity of their reflectors and grating make these the most expensive out of the three types listed here – typically costing between $400-1,500.