How Does A Scope Work? (Beginners Guide)

A basic scope can be described as one with a front lens (objective lens) followed by a tube and another lens (ocular lens). Inside, you also have an erector lens and a magnifying lens. It is safe to say that a rifle scope works very similar to that of an astronomer’s stargazing telescope. But how do all these parts function in the proper orientation to provide the visual image we obtain from a scope? In this article we explain how a scope works, the different types of scopes and different critical aspects such as first focal plane and second focal plane scopes. 

How Does A Scope Work?

picture of a rifle scope with orange and green background

Most of the traditional rifle scopes, like budget LPVO rifle optics, create a magnified image using the same technology.

  1. Light passes through the objective lens and reaches the focal point. The larger the objective lens diameter, the better the light transmission and, hence the brighter the visual picture is.
  2. The image is inverted, this is where the erector lens comes into play. The erector lens flips the image back into the correct orientation.
  3. The image then reaches the magnification lens. In variable power scopes, the image size increases or decreases based on distance from the ocular lens. The higher the scope magnification, the closer the magnification lens is to the ocular lens.
  4. With fixed power scopes, the magnification lens is in a fixed position and is unable to move. But more on this later in the article.
  5. Depending on whether you have a first focal plane scope (FFP) or a second focal plane scope (SFP), the reticle will either be in front of the magnification lens or behind it, respectively.
  6. Finally, the light passes through the ocular lens into the eye, and depending on how good the scope’s eye relief is will determine how easy it is to achieve proper sight picture.

First Focal Plane vs Second Focal Plane Scopes

As already mentioned, with an FFP scope, the reticle is on the front of the magnification lens. Enabling the reticle to change size proportionally to that of the magnification setting in order to keep a constant relative size throughout the aiming process. So, in other words, the reticle increases in size as the magnification increases. Remember, the best magnification for hunting & other use cases depends on your specific rifle and shooting conditions!


An SFP scope’s reticle is placed behind the magnification lens, meaning that the reticle will remain the same size even when adjusting the magnification settings.

For more on the benefits and drawbacks of each type of scope, feel free to read our detailed article on First Focal Plane vs Second Focal Plane scope.

What Is Eye Relief?

picture of shooter demonstrating eye relief

Eye relief is the distance between the outer surface of the ocular lens to the position where the exit pupil of the eye is formed. This is one of the first things I check on my 350 Legend Rifle Optics before I go out in the field.

If the scope’s eye relief capabilities are too little and your rifle is a high recoil cartridge, a possible injury might occur. With too much eye relief, the rate of target acquisition is compromised.

This is why proper eye relief is an extremely important factor to consider before buying a scope, and I strongly recommend you read our detailed article on everything regarding eye relief before purchasing a new rifle scope.

Scope Parallax Adjustment

Parallax error is the inconsistency in a scope’s view when moving your eye from one side of the eyepiece to the other side. Causing the scope reticle to appear out of focus in relation to the target you are aiming at. Resulting in a disproportion between the target and the reticle’s crosshairs, as if the target is moving relative to the reticle, putting accuracy at risk. This can affect the best night vision rifle scope or traditional scopes as well!

Parallax adjustment is basically fine-tuning the focus on the riflescope so that the shooter’s eye and the target are on the same focal plane, and is done to prevent the above from occurring. Using the parallax adjustment knobs typically located on the side of the scope, you will adjust the reticle until it is crystal clear. When doing the movement test, the crosshairs are no longer moving off the target. We also have a how-to guide on making parallax adjustments to make things easy!

Parts Of A Rifle Scope

1) Scope Rings

Scope rings are used to mount and secure the rifle scope to the rifle, ensuring that the optical system is unable to shift when firing a shot or from a collision. Scope rings are a must & you also need to know how to mount a scope on a rifle the right way!

2) Windage and Elevation Knobs

The windage and elevation knobs are typically located in the middle of the scope, with the windage knob on the side and the elevation knob on top.

The windage and elevation turrets are used to make windage and elevation adjustments in order to align the aiming point and point of impact with each other to ensure accurate shooting.

The windage adjustments are used to make horizontal shifts, and the elevation knobs adjust the vertical plane. Each knob will have information regarding the direction and the “click value,” which is typically in Minutes of Angle (MOA). Learning how to adjust scope turrets is very important! 

3) Objective Lens

The objective lens on your Tactical Scope for AR-10 308 SHTF is located on the front of the scope and held tight by the objective bell. It is mainly responsible for determining the quality of the visual sight picture by regulating how much light and what frequency and wavelength of light are transmitted into the scope. An objective lens with a larger diameter will transmit more light and thus allow for a brighter sight picture.

Many rifle scope manufacturers put multiple lens coatings on their objective lenses to minimize glare and maximize light transmission. The quality of the manufacturer’s lens and the coatings will determine how bright and detailed an image will be to the shooter. And if you want your scope to have a clear image, be sure you are cleaning scope lenses as well!

4) Scope Tube

The scope tube is the frame and body that houses all the individual lenses and target turrets. Most scope tubes are built from a lightweight, ultra-strong material such as aircraft-grade aluminum to provide high-performance results. Some of the scopes built for a scope magnification for 500 yards are often larger than lower magnification scopes.

5) Eye Piece / Ocular Lens

An eye piece or the ocular lens is the rear lens found closest to that of the shooter’s eye. It is where the light escapes from the scope and is transmitted into the exit pupil of the eye. The quality of the eye piece is important as it will contribute to how easy it is to shoot with the scope.

It is also important because it determines the eye relief, which determines the scope’s use case. Most scopes used for bolt action rifles have a longer eye relief as the recoil is higher, and scopes for the AR platform typically have a short eye relief or unlimited eye relief, as is the case with a red dot sight.

6) Power Rings

The power rings are used to make magnification adjustments to the scope. It is typically found on the smaller ocular lens as a rotatable ring for easy adjustment. The turning range of the power ring will depend on the magnification of the scope. Typically with high magnification scopes that have a magnification range of 5-20x, the power ring range can be 1/2 of the ocular lens’s eyepiece.

Different Types Of Rifle Scopes

1) Fixed Power Scope

As the name suggests, in a fixed power scope, the erector lenses are held in a stationary tube and are unable to move. This approach allows for a very minimalistic design approach in terms of the body and adjustment knobs, allowing for a lightweight and streamlined scope that has increased maneuverability capabilities over a variable power scope.

2) Variable Power Scope

A variable scope allows for the adjustment of the magnification typically done by the power rings. When turning the power rings, the magnification lens will either slide closer or further from the ocular lens, depending on if you are increasing or decreasing the magnification, respectively.

The benefit of using a variable power scope is that it enhances the range capabilities over a fixed power scope or iron sights, allowing a hunter to make accurate shot placements at variable distances

3) Night Vision Scope

As opposed to a thermal scope which uses a heat signature for detection, a night vision scope uses a digital sensor to amplify or enhance the surrounding ambient light and convert it into a visible image, either in green phosphor or black and white.

A night vision scope does, however, require some level of ambient light to function optimally. These types of scopes are typically used for varmint hunting or hunting in bright moonlight conditions and early dawn or late dusk. I personally use Night Vision Scopes for Coyote Hunting in the fall months!

4) Hunting Scopes

Most hunting scopes are variable scopes that allow the hunter to have long-range shooting capabilities by increasing the magnification. The scope is built from highly durable materials, able to survive the elements and collisions. These scopes have a longer eye relief to prevent the shooter from an injury obtained from the rifle’s recoil.

5) Competition Shooting Scopes

Competitions shootings scopes are high-end scopes typically fitted with many additional features. They are built for target shooting at short and extremely long distances. These modern rifle scopes typically have a bullet drop compensator, range finder, windage and elevation adjustments, etc.

6) Spotting Scopes

Spotting scopes are used for outdoor activities such as birdwatching, scouting deer, or other tactical use cases. These scopes are monocular, meaning only one lens, and thus only one eye is used to see through the scope. The Best Long Range Spotting Scopes are very effective tools that every hunter should use!

A spotting scope provides a higher detailed sight picture than a binocular but also results in faster eye fatigue.

Frequently Asked Questions

How does a scope work if its above the barrel?

When mounting the scope, the shooter adjusts the scope to align with the rifle. So that when a bullet is fired, the point of impact will be exactly as indicated by the scope.

How does the power work on a scope?

The power range works by adjusting the power rings. When adjusting to a higher magnification, the magnifying lens will move closer to the ocular lenses, therefore increasing the magnification, and for lower magnification, the opposite is true.

Do you close an eye when using a scope?

An experienced shooter such as snipers keeps both eyes open as it increases their peripheral vision. However, most hunters and target shooters close one eye to increase focus on the other eye, allowing for a more precise shot.

What happens if 2 bullets collide?

If these two bullets have the same momentum force, then both would have zero final momentum after colliding, making them stop and most likely break up into little pieces.

What size scope do I need for 300 yards?

A good scope for 300 yards will need a magnification range of between 3-9x to ensure accurate shot placement.

The Bottom Line

A rifle scope has the same basic components as a telescope used for stargazing. And even though all these types of scopes have different features that distinguish them from each other, they all function on the same principle. So if you are in the market for buying a gun scope, it is important to take all these factors mentioned in this article into consideration.

About the author

Patrick Howard

I have been working as a gunsmith for 20 years. Rain, fog, moisture, high temperature, or even snow are all the things a product must withstand in order to be recommended by me.

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