Non-focusing sights

So far, all the riflescopes I mention are “focusing” optical instruments. What that means, is that the scope re-creates an image of the object in front of it somewhere (there are a couple of focal planes inside the scope where the image is re-created). Then that image is effectively “cast” back out by the riflescope’s eyepiece for your eye to pick up and re-create again on the retina of your eye.  The distance where your eye has to be to pick-up the entirety of the image is called “eye relief”, and it is typically between three and four inches (75 to 100mm).  In order to see the image presented by the scope, your eye has to be in a specific spot behind the riflescope. There is some leeway to the eye position (sometimes referred to as “eyebox”), of course, but if you happen to place your eye too far off, you won’t see much.

Non-focusing sights are the ones that do not have that eye positioning limitation, but they also do not offer any magnification. These are non-magnifying sights that include various red-dot and holographic sights. There are a few 1x (unity magnification) focusing scopes out there that are usually identified as 1x prism sights. They have pretty flexible eye position requirements, but they are still not quite as lenient in that regard as true non-focusing sights.  They do offer some significant advantages for people with astigmatism.

Red-dot and holographic sights are designed for super-fast target acquisition with both eyes open and work well for close-range tactical applications. These are the sights your most frequently see in pictures from Iraq and Afghanistan mounted on the army issued M4 carbines. US military issues a large number of Aimpoint red-dot sights and Eotech holographic sights. They represent the two most common types of non-focusing sights out there.  Since the success of these two brands, many others jumped into the fray.  In terms of the battle of technologies, red dot sights (aka reflex sights) are by far the more prolific.  Holographic sights, in principle, represent some very interesting advantages in terms of complex reticle designs and use with magnifiers.  However, holographic sights have small lasers inside, while reflex sights use LEDs.  That gives reflex sights substantial advantages in battery life.  While they did not start out that way, as of 2016, there are dozens of reflex sights out there that you can leave on and expect the battery to last for a couple of years.  Reflex sights can also be made smaller and, personally, I strongly prefer compact red dot sights to the full size ones.  Holographic sights, on the other hand, work better with magnifiers and offer some other advantages.  Ultimately, it comes down to what you prefer. 

Effectively, all you are trying to do with a sight like this is look through a short tube that makes up its body. If your eye is positioned along a straight line behind the sight (or close enough to it), you’ll see a red dot, which is your aiming point. In order to have reasonably fast target acquisition, the dot is pretty large (although this varies between models). Unfortunately, a large dot that aids target acquisition also makes it harder to shoot accurately at longer ranges. Still, a red dot sight is easily good enough to shoot deer-size targets within 100yards, and, in the hands of a skilled shooter, a fair bit further than that.

Aiming with the Eotech, in principle, is similar to aiming with a reflex sight: look through the squarish tube and place the reticle onto your target. However, the reticle of the holographis sight can be any pattern, like the circle-dot arrangement on most Eotechs, rather than a large dot of most red dot sights:

With the Eotech, you are looking through a holographic screen and, in some circumstances, the reticle can appear pixelated which some people find distracting. However, on balance, both Aimpoint’s large dot and Eotech’s circle-dot are very effective.

In recent years, in order to extend long range capabilities of red-dot sights, a few companies introduced magnifiers. These are essentially short monoculars with 3x or 4x magnifications that can be placed immediately behind a red-dot sight. When not in use, they can be either removed or flipped aside.

Lastly, there is quite a number of so-called “micro red-dot sights” on the market. These are simply red-dots small enough to be mounted on handguns or as secondary sights onto riflescopes. Aside from tiny size, their operation is not different from any other red-dot sight.