How Does a Rifle Scope Work ?


Anyone who loves firearms knows the sport is full of wonderful anecdotes and narratives. One of the best phrases says hunters can hit any target using a mediocre rifle with a great scope, while a hunter with a mediocre scope will have trouble hitting the same target with a great rifle.


There’s no doubt that using a scope makes it easier to hit targets at a longer distance with much greater accuracy, because it helps to align the rifle with the target. A scope will improve your hunting or shooting accuracy significantly, and the quality of the scope you choose can actually matter even more than the quality of your rifle itself.


After all, a shooter can much more likely hit a target using a great scope with a mediocre rifle, but even the best rifle won’t be of much use in hitting targets with a bad scope.

Choosing a scope depends on precisely what it is that you want to shoot, as there are different types of scopes adapted to different kinds of shooting.


The best scope for deer hunting differs significantly from the best option for target shooting, so keep this in mind before investing in the wrong scope and finding it of limited use for your needs.

The moral of the story; optics mean everything.

Different types of rifle scopes

Rifle scopes are available for every budget, though of course you’ll probably want to try and find the best quality model which you could afford if you want to improve your shooting accuracy.

The magnifying power of a scope directly affects what you magnification you will view objects downrange. Some scopes are fixed power, which means that you cannot adjust its magnification. Others are variable power, allowing you to magnify things in a range of the number of times larger than they would be visible to the naked eye.


For instance, a fixed magnification scope with a power 4 times that of the naked eye would be listed as 4x.


Variable power scopes come with a range, and so you might see one that’s listed as 3-9x for example. The other number on a scope represents the size of the objective lens, which is typically measured in millimeters.


While fixed power scopes don’t give you much to fidget with, variable ones have a power ring that you can adjust to bring it into the correct focus.

Most manufacturers design their scopes for use at a distance of roughly 100 yards, though you should be wary of parallax error when you’re actually using it. This is when your eye position is not where it should be, which will put you off target.


Parallax error tends to become far greater at higher magnifications though, meaning that it’s more something that snipers have to worry about than your average deer hunter or target shooter. Still, most scopes come with a parallax adjustment feature in case you ever end up needing it.


Firearm scope technology improves as often as optics will allow. New rifle scopes with targeted acquisitions of better than 2000 yards are now quite common. What has evolved is a collection of features such as night vision, laser sighting, thermal imaging, and computerized digital tracking.


The inner workings of modern rifle scopes are a compelling exploration into advanced optics and precision manufacturing. Modern scopes are leaps and bounds more intricate than just a few years ago.


There are rifle, shotgun, and handgun scopes for any condition and terrain. Hunters may need a scope that can target ten yards to sixty yards out for most of their covered conditions.


Deer hunting in flat territories like Texas or Oklahoma, you need a scope accurate to 300 yards and out. Target shooters love seeing shots made at 1000 yards or more.


There are hundreds of various scope configurations, materials, sizes, and price points. Manufacturers around the world have dozens of scope models, adding more every month. I will spare you the endless opinions on what manufacturer, scope, or magnification is best—concentrating more on their inner workings.


What is inside a rifle scope?


how-a-rifle-scope-works

A rifle scope, at the bare minimum, is a tube machined from a solid block of high-grade aircraft aluminum. The main outer tube can be a one or two-piece construction.


Main tubes are made from steel and titanium as well. Aluminum offers the best properties, while steel is heavy and corrosive. 


Eliminating Fog and Condensation


Eliminating fog and condensation is always are problem. Modern scopes are most commonly filled with nitrogen, argon, or a combination of argon and krypton gas. Scopes go through a rigid process to control any leakage and are usually sealed hermetically. 


Given the resemblance between the two, it probably won’t surprise you that the inside of a rifle scope and that of a telescope work along similar principles.


Scope Lenses

Scopes contain up to eight separate lenses with areas for magnification, orientation, and an aiming instrument called the reticle. At a minimum, rifle scopes will have:


  • Objective Lense
  • Erector Lense
  • Megnifying Lense
  • Ocular Lense

A rifle scope has an objective lens in the front, which allows light to come in; a focus lens, for focusing objects in the scope; and an ocular lens in the back, which is what actually allows the shooter to see what they’re aiming at.


There are also other lenses inside of a scope, but we’ll get to those.


How the Lenses Work

  1. The objective lens is positioned full forward in the scope tube. 
  2. The target image is transmitted through the objective lens to an erector lens assembly.
  3. The target image is flipped to the proper orientation by the erector assembly and sent through to a magnifying lens, then on to the ocular lens.
  4. The ocular lens, the lens closest to the shooter's eye, displays your target. 


The basic description above shows you how essential optics are with any scopes.


Companies such as Nikon, Zeiss, and Leupold offer some of the best optic glass and coatings on the planet.


Pay close attention to the glass and its coatings when making a purchase decision. 


Let's study in close detail what the objective lense and the erector lense do.


  • An Objective Lens is housed in the objective bell, which is the large part of the tube body farthest from the shooter's eye. Hunters need to be aware of the size of the Bell Housing and mounting on your rifle. If the bell housing is too large, you may need higher mounting rings or a different scope. This obstruction can cause poor eye alignment and compromise a comfortable cheek and weld method. Do not forget the quality of the Objective lens itself. Make sure it is excellent material and has a coating to improve target transmission. Superior quality glass material with excellent coatings reduces reflection and glare, a concern when picking out your target at sundown. Weight is another issue with a larger objective lens, stick with the 40 mm lens if extra weight is going to be a problem. 
how a rifle scope is structured
  • Erector Lens Assembly is an internal tube configuration containing the reticle, erector lens, and magnification lens. Once the target image passes through the reticle, it hits the erector lens assembly, which properly orients the image and sends it on to the magnification lens. Some technologies have the reticle built-in with the erector assembly. Reticles in front of a magnification lens is a first focal plane scope, and reticles behind the magnification lens are second focal plane scopes. Scope manufacturers have separated the erector lens assembly from the reticle and magnification components while others have combined these features. Stick with a quality company, and you should be fine with either configuration.

What is SFP (Second Focal Plane) and FFP (First Focal Plain)

Before moving on to the ocular lens assembly, it is essential to have a brief explanation of first and second focal plane technologies in rifle scopes. An SFP scope has the reticle placed behind the magnification lens. With this configuration, objects appear to be the same, no matter the magnification. An FFP scope has the reticle placed in front of the magnification lens, and objects appear to change as the magnification goes up or down. 


SFP scopes have been the standard technology for decades, while long-range shooters have used the FFP configuration. 


FFP strategies are gaining favor as optics, firearm materials, and ammunition have improved, allowing for long-range hunting. Long range hunting to some is 40 yards, while others it means 400 yards. If all your shooting and hunting is done at the highest magnification, SFP scopes work fine. Before buying an FFP scope, look at the reticle at all power settings. 

  • Magnification is expressed as a number corresponding to the size of an object at a precise distance compared to the object observed through the naked eye. The target image is captured by the magnification lens and "adjusted by the hunter" before being sent through to the ocular lens assembly.

vortex scope on ar10

The power ring on a rifle scope lets the hunter adjust magnification up or down. The scope's magnification levels will be indicated as a 2X up to 25X and beyond.


A 2X magnification means your object is two times closer than the human eye perceives and a 25X is 25 times closer than what a human eye can recognize. 

  • The lens facing the shooter is the Ocular Lens or Lens Assembly. This lens focuses the target image from the objective lens and erector assembly. When determining the best rifle scope for your demands, make sure to examine the quality of the ocular lens, the eyepiece assembly and its coatings. Companies such as Nikon, Zeiss, and Leupold have developed advanced coating technologies. As an example, Nikon's SeeCoat Lens Protection provides world-class optic protection. Another consideration, make certain the builder has used quality O-Rings in each of its optical assemblies to dispose of water and fog. 

Types of Reticles To Improve Your Aim 

The reticle in a rifle scope is the crosshairs or aiming point you see when peering through the ocular lens toward your target image. Read the brief narratives above describing a FFP and SFP scope, to get a sense of how does a rifle scope work and reticle placement inside the main cylinder. 

The reticle is typically either made up of fine wires or simply etched onto a glass plate. Reticles come in a variety of different styles, many of which are designed with specific purposes in mind.

crosshair of rifle scope

Crosshair of Scope

There are nine specific reticles available: 

  • Original; single vertical and horizontal crosshair
  • Dot; single dot in an enclosed circle outline 
  • German reticle; crosshairs tapering off toward the center
  • Duplex; thick crosshairs with a weakened center
  • BDC; Bullet Drop Compensation
  • Mil-DOT; ballistic reticle measured in Milliradians 
  • Non-illuminated; simple black

  • Illuminated; lighted 

  • Christmas Tree; shaped like a tree

The reticle is either placed in front of or behind the magnifying lens, with the placement making some difference in a variable power scope. If it is in front of the magnifying lens, it will appear to change size when zoomed in. If it is behind the magnifying lens, however, it will appear the same size regardless.

A scope is held onto a rifle using what are known as scope rings, with several variations as to how exactly this is done. Mounting rings in their most basic form are two-piece clamps, often encircling the rifle.


There is an enormous assortment of reticles from third-party vendors as well as each scope manufacturer. Some reticles are straightforward with a three post design, while others have calibrated designs along with MIL-DOT and lighted and unlighted. Choosing the right reticle for your needs depend on the hunting you propose, and an abundance of personal inclination and conditions thrown in. 

Athlon Optics Argos BTR Riflescope 6-24 x 50 First Focal Plane -Reticle V iew

Reticle Views

 

Reticles have become technologically advanced just the same as the optics. Reticles are often made of wire; however, glass-etched reticles are becoming prominent within the hunting community because of their durability and unbreakable reputation. 

 

Hunters can buy reticles for the various game they are after. Target shooters can have their aiming points tactical in nature or laser sighted.


Horus, a specialized optic reticle maker, builds incredibly advanced and intuitive aiming points that do not require a holdover or click to make aiming adjustments. Horus specializes in long-range tactical sniper reticles. 


How does scope magnification work?


Light passes through the objective lens (which is away from the user), which in turn transmits light to the erector lens. The erector lens flips the image (so that it won’t appear upside down) and it passes to the magnifying lens.


The light finally travels through the ocular lens, through which it is visible to the shooter. Needless to say, the most important parts of any rifle scope are its lenses.

How do scope adjustments work?


Good External Adjustments Are The Key To Good Targeting  

Rifle scope adjustments are made from various turrets and dials found on the top and sides of the primary tube. 

  • Elevation Adjustment (bullet impact, up or down) 
     

  • Windage Adjustment (bullet impact, left or right) 
     

  • Parallax (target focus) 

  • Magnification

A rifle scope will allow you to adjust for windage and elevation, so that you can account for wind direction and distance. Windage is the horizontal plane, while elevation is the vertical one - which is pretty logical if you think about it.


Some reticles are designed with markings to help shooters figure out where their shot will actually land at different distances, typically further than the zero. These types of reticles thus mean that there would be no need to adjust the scope’s zero.

What do the two knobs on a scope do?


The two knobs allow you to actually adjust the scope for windage and elevation, which have been defined in the previous paragraph. One knob is dedicated to windage, and the other to elevation.

Rifle scope adjustment knobs

Scope Adjustment Knobs

Elevation Knob

Elevation adjustments change the bullet point of impact up or down relative to the aiming point. Most elevation turrets are situated at the top of the scope. The erector assembly serves as the interface between elevation and windage adjustments. 

 

Elevation adjustments are set when you first Zero in a scope, or the target distance has shifted.


Here are a couple of excellent YouTube Videos to help in creating your zeroing process:

How to Mount, Balance, and Zero a Precision Rifle, by West Desert Shooter.

If your point of impact for the bullet is low, rotate the turret counter-clockwise to move the direction up. The inverse is true if your bullet impact is high of the target. For most scopes, each click of the turret dial represents angular change.


As such, each click of the turret is ¼ MOA or Minute of Angle. Here is an outstanding article illustrating the properties of MOA and why shooters need to understand the principle to improve their accuracy. 

Two Shot Sight-In by the National Shooting Sports Foundation.

You may be able to turn these with your fingers in some models, while other models require you to insert something like a coin to adjust the knob.


These knobs come with markings so that you know what you’re doing, and are known as “turrets”.

Picking the right scope for your rifle can mean the difference between excellent and disappointing performance, regardless of how good or mediocre your rifle is.


In order to pick the right scope for your needs, you need a basic idea of how scopes function or you’ll likely end up quite lost in the buying process and quite possibly get the wrong model for your needs.

Windage Knob

Windage adjustments are made with the turret commonly found to the side of your scope. Windage moves the bullet point of impact left or right. Windage adjustments with distances of no more than 60 yards, are seldom an issue. However, if you are sighting in at 200, 300 or more yards, gusts of wind can alter the track of a projectile. 

 

creedmoor rifle scope zeroing

After adjusting elevation or windage, it is a clever idea to make your final turn in a clockwise direction. This routine makes certain the turret adjustment springs are providing good contact with the erector lens assembly. 

 

Another tip: whatever change is farthest out, make that adjustment first. As an example, if your windage is four clicks and elevation is two clicks, adjust windage first. Whatever adjustment is made second reduces the modifications you can make. 

Parallax Knob

Parallax errors are modern conditions brought on by extreme technological advancements in rifle scopes.


Parallax describes a condition where the reticle offsets the focal plane of your target. If your scope exhibits parallax, you see an optical illusion. 
 

To identify parallax; gaze into the scope. If your reticle changes target position while you change your gaze slightly, parallax is not properly compensated for at the range you have set.


 In simpler terms, the reticle causes the target image to appear as 3D. If there is no parallax, the target image appears to be painted on, and the reticle never changes relative to the image. 

 

finding optical zero with mirrors

Reflection Of Reticle View

Now that you are thoroughly confused, do not over think parallax errors. Most scope builders have compensated for the problem in the optics. Some builders have added a parallax adjustment turret if they know tits scope will have errors. 

 

The condition of parallax is rarely encountered at shorter distances with less complicated scopes, parallax is more an error for longer distances. Do you require a scope with a parallax adjustment? Probably not. However, if you shoot for sport or hunt at long distance, find out precisely what parallax is and how it influences your target and scope. 

Magnification

Adjustments for magnification are made by a ring just forward of the Ocular Lens assembly. Some scope designs require the shooter to adjust the entire ocular lens assembly.


Remember, in first focal plane scopes, the reticle changes size in relation to the target through all magnification settings. Second focal plane scopes, reticles stay the same size through the magnification range. 

best compact scope

 If magnification is a pre-requisite factor when making a scope purchase, it is essential to choose based on your hunting conditions and terrains. 


FFP scopes are ideal for long-range shooting and hunting, and the reticle is vital to success. SFP scopes have fewer moving parts and so are more robust at lower power. 

 

Hunter's tip: lower magnification settings will make you a better shooter, because there is less obvious movement of the target. 

Important Concepts to Know


Dedicated shooters and hunters understand the principles of Exit Pupil and Eye Relief and are always asking themselves how does a rifle scope work to my advantage. If you love the sport of firearms, learn these two concepts and how they can improve your accuracy. 

Exit Pupil

When you are looking through a rifle scope at arms distance, the small circle of light seen in the ocular lens is the exit pupil. Calculating the exact size; divide the diameter of the objective lens by the magnification of your scope. 

 

Why is the exit pupil important? The exit pupil is a virtual aperture. In optics, the aperture is the opening in a lens (objective) which light passes through. In the case of a rifle scope, the larger the exit pupil, the more light can enter your eye. 

best rifle scope under 500

 

The logical conclusion find a scope with the largest objective lens, so I have a large exit pupil. The problem with this thinking, the human eye is only 5 to 7 mm in diameter. An exit pupil much larger than 7 mm would be more light than the human eye can handle. 

 

Again, hunters need to know their best hunting situations when choosing a scope that will meet demands. Knowing the scopes exit pupil becomes important in low light situations like dusk or dawn hunting. Choose a scope that has, at a minimum, 5 mm of exit pupil diameter with various magnification settings. Take advantage of all available light. 

Eye Relief

Eye relief is described as the distance from the ocular lens to your eye taking in the full field of view (FOV) exit pupil. Eye relief is the optimal image produced by your scope. If the eye relief is too close, the image becomes fuzzy, too far and all you see is a dot in the middle of your ocular lens. 
 

The industry average for eye relief with a fixed scope is around 3 ½ inches. Low to high end magnification on variable scopes, the distance is plus/minus 2 ½ inches. Eye relief decreases as magnification increases and vice versa.


On variable scopes, such as a 3x by 9x, eye relief is greater at 3x than at 9x. 

 
 One of the most important considerations when matching a scope to your rifle is the recoil. High powered rifles with a lot of recoil and short eye relief could cause a problem with the scope hitting your eye or scope bite . 

marine sniper scope

 

It is not a good idea to mount a scope on the rifle, lock it down, and force the shooter to acclimate to the scope. This leads to poor marksmanship. When you are mounting your scope, it is best to determine where the shooter's cheek sits and what is the most comfortable firing position. Once this has been set, install and lock down the scope. 

Conclusion

The main design of a scope has been unchanged in the last few hundred years. Technology, materials, and advanced manufacturing methods have contributed considerably to the evolution of firearm scopes. 

  

Rifle scopes are some of the best engineered, technologically advanced products on the planet. World brands such as Nikon, Leupold, and Zeiss have brought their considerable optic technological advancements to bear on the industry. Companies such as Vortex and Nightforce are taking scope technology to unimaginable levels. 

 

Choose the best scope for your needs based on some of the concepts described above. Remember, the quality of the optics and their coatings play the most important role in hitting your target. Quality optical glass can last a lifetime if cared for properly. 

 

There is a rifle scope to match any terrain, condition, or hunting situation. Choose Wisely‼! 

For Different Types of Rifle Scopes Check Our Guide:

1.Visit RifleScope Reviews for More Info

Related Posts

How to Choose a Rifle Scope

What is Eye Relief on a Scope

George Grey


Being an avid outdoorsman since I can remember, my passion for survival, hunting and the outdoors has grown every year. I love being out in the country and living off it whenever time allows.

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