How a scope works and what are its parts

The characteristic cross (properly known as “Reticle”) that we see in movies when a shooter puts his eye up to the lens is the typical image that we have of a rifle scope. But really, what actually is a riflescope? Where does it come from? And how does it work?

Telescopic sight has become the hunter’s, the shooting sports athlete’s and the sniper’s best friend, because it allows them to make those legendary shots without having to be detected.

As we all can imagine, the appearance of scopes revolutionized and completely changed the rules of the shooting game. For example, in wartime, they give their users a huge advantage if they are positioned at a far distance from their enemy. In the world of shooting sports, they have opened the doors to the creation of new disciplines. Telescopic sight has also made it possible to hunt new species of game that were previously considered impossible due to their swiftness.

A very good friend of mine expressed this phenomenon the following way: You can give yourself the luxury of settling for a bad rifle, bad ammunition and having bad aim… but if you have a bad scope then you automatically cancel out all of your skill and the quality of your equipment.

In this article we will explain what a scope is, how it works and what parts it has.

What is a scope and where does it originate

A rifle scope is an optic system whose objective is to amplify or magnify an image in order to optimize a shooter’s precision while shooting distances that exceed his eyesight.

The first to experiment with this concept was August Fielder, circa 1880 in Stronsdorf, Austria where he was a high commissioner to Prince Reauss. By the Prince’s request, Fielder designed and created the first prototype that would eventually originate the modern riflescope that we know and use today.

A number of manufacturers began to apply August Fielder’s newfound discovery and began to perfect the original prototype. Amongst these manufacturers was the notable Karl Robert Kahles who began to produce and sell artisanal pieces made by hand in 1898. That is why the Austrian brand, Kahles, is considered the oldest manufacturer of rifle scopes in the world.

This new product’s success grew like wildfire to finally become a world renowned name during the Second World War.

The anatomy of a rifle scope

The first step to comprehend how a riflescope works is to know its parts perfectly. We want to be meticulous and specific for you so we will begin by dissecting the external parts from the internal ones:

External parts of a scope

1. Quick focus adjustment (Diopter adjustment): It is used to adjust the sharpness of the scope to our eye. Each eye sees differently and therefore the first thing is to fine-tune the diopter setting.
2. Eye bell/Eye piece: This portion of the scope is found closest to the observer’s eye, it’s the part through which you peer into the scope and in the ocular lens is housed.
3. Illumination adjustment knob: This accessory is not found in all scopes. The reticle illumination control (located on the side of the main tube) can modify the brightness level of the reticle’s lit areas and on occasion can even change the reticle’s color in order to favor visual contrast. This system serves as an aid that heightens a gunman’s performance in low light conditions and is especially useful for long range hunters.
4. Magnification power ring (power adjustment ring, zoom ring): For a scope with adjustable magnification power, this ring permits the user to increase or decrease the power or “zoom”, between its ranges. This also is a feature that belongs to certain riflescope models.
5. Main body: A rifle scope’s main body takes the shape of a tube. Its function is to protect the scope’s internal optic system and it also gives room to the mounts, bases or rings that allow a scope to be attached to a rifle.
6. Elevation turret knob: Often located on the top side of the scope, the elevation turret knob allows the gunman to regulate and move the reticle vertically, up and down. One would use it when he needs to calibrate the scope because it is pointing higher or lower than it should.
7. Windage turret knob: The windage turret knob is commonly located on the (left) side of the main body tube and by adjusting it you will move the reticle horizontally; side to side and left to right.
8. Objective bell: It is easily recognizable because it is the scope’s widest portion, fixed at the furthest end from an observer’s eye. It serves as a light collecting apparatus and within its interior is the objective lens.
9. Parallax knob: A feature that is especially useful for long range scopes, the parallax knob’s function is to correct the parallax error and fine tune the image’s focus until a clear picture of the reticle is achieved. When an image is correctly focused, this phenomenon is eliminated. Unfortunately, not all scopes possess this accessory.

Internal parts of a scope

1. Objective lens: This is the window through which ambient light can enter the scope’s internal optic system and consequently is refracted to the ocular lens. As an objective lens’ diameter increases, so does the amount of light introduced into the scope and your eye. The objective’s size is measured in millimeters.
2. First focal plane optic: Situated inside a scope’s main body tube, this lens serves as the first single finite point where the rays of light travelling through the objective lens will converge.
3. Second focal plane optic: Also found within the main body tube, the before mentioned rays of light will once more converge thanks to the second focal plane optic. Together, both lenses are responsible for creating a clear and focused image.
4. Reticle: This image, usually found in the shape form of a cross, serves as the gunman’s guide whilst taking a shot. The reticle is situated between the first and second focal plane and is normally printed on to one of these lenses. That is why the reticle is usually referred to as being on the first or second focal plane. There are numerous types of reticles.
5. Erector system: This system is found between the first and second focal plane optics and it holds the magnifying lenses and reticle components. It moves around inside the main body tube in order to control magnification and point-of-impact.
6. Illuminated reticle: In order to have an illuminated reticle a riflescope must have two internal reticles. One of them (the reticle described above) will situated on one of the two focal planes meanwhile the second, illuminated reticle will be located on the other. Based on where the reticle is mounted the scope will be referred to as a “front (first) focal plane” scope or as a “rear (second) focal plane” scope. Regardless, a shooter will never be able to distinguish one from the other. Only specific scopes possess the advantage of having an illuminated reticle.
7. Ocular lens: Located at the rear of a scope, this lens finalizes the light-refraction process making the sight picture visible to the observer.

It is very important to mention that generally a scope’s lenses are covered by an antireflection membrane that decreases the amount of light that is reflected back to the exterior. This serves as a precautionary measure that will prevent the shooter’s location from being given away and it also maximizes the amount of light that enters through the objective lens, favoring the creation of a sharper and clearer image. The interior of the scope is sealed in order to avoid the entrance of rain, humidity and dust into the interior which result with the opacification of the lenses.

It is also important to mention that initially, a scope’s main body tube was made out of iron but now they are fabricated from much lighter material like carbon or aluminum alloys.

How a riflescopes works

After having seen the anatomy of a scope in great detail, learning how it works becomes a much easier process. Nevertheless, for some it can still prove to be an ordeal to completely understand the laws that govern the refraction of light. Therefore we have concocted a concise simplification that should help:

The interior of a rifle scope works practically the same way as your conventional telescope. The rays of light that pass through the objective lens are met with different lens inside of the scope. The result of this interaction is a clear and sharp image correctly refracted on the ocular lens where it will be perceived by the observer.

How a riflescope’s turrets work

In regard to a riflescope’s turrets, we can easily identify the elevation turrets as those who are located on the top of the scope and the windage turrets the ones that or found on the scopes side.

The elevation turret moves our reticle up or down, this allows us to calibrate or make adjustments to our riflescope when we are taking long range shots.

The windage turret moves the reticle left or right, also contributing to the scope’s calibration. This turret generally does not need to be modified when it comes time to take an accurate shot.

Finally, you may find a third turret on your scope’s right side, known as the parallax knob. This knob is used to correct the parallax error. For more information about the parallax phenomenon you can consult our article that explains what parallax is and how to correct it. For more information on what parallax is, see our article on what’s parallax is and how to correct it.

Type of reticles

Today, each brand of optics designs its own crosshairs and therefore there are countless crosshairs on the market.

However, we are going to show the most well-known designs in order to be able to have a notion of the types of reticles that exist.

First we have the classic designs :

It can be seen that among these models there are almost no references , since the emergence of references in the reticle is quite modern. They are generally still in use and are especially used in hunting scopes. The most popular are reticle 1 (also called German) and reticle 4.

Then we have the modern types of reticles that are mostly referenced . This means that they have multiple references that help determine distances or make corrections in distant shots. These are some of the most popular:

It should be noted that there are many more, but that among the best known we have the duplex that could be understood as an improvement to the classic 8 reticle. And the Mil-Dot, iconic reticle , which was the first from which distances began to be determined thanks to the references in the crosshairs of our sights. It is so called because the distance between the dots in the drawing is equal to 1 MIL or MRAD (Milli radian).

About the calibration and use of a riflescope

We wanted to further enrich this article and to do so we decided to add basic notions on how to calibrate and use a riflescope correctly. If you want to know more about the process of calibrating a scope, we recommend our article on how to calibrate a telescopic sight scope

There are four important adjustment parameters that one must have in mind while taking aim for a shot. Each parameter one be manually set using the turrets and dials located on the scope’s exterior. These parameters are:

1. Elevation: It determines how high or how low the reticle’s horizontal line is set.
2. Windage: It determines how far left or right the reticle’s vertical line is set.
3. Magnification: The modification of a scope with adjustable magnification allows the shooter to see distant targets with greater ease.
4. Diopter: It allows a faraway object to be seen with great detail. For example, if your scope is focused at 25 meters (27 yards) you will be able to see any object situated at that distance very clearly, but anything closer or further away will appear blurry.

It’s very important to clarify that there are external factors that can alter the trajectory of our projectile. If we had to name a few they would be humidity, wind and the effect of our planet’s natural rotation but these are not alone and there are numerous other factors as well.

We hope this article has proved to be useful for you.

Good shots!

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