A rifle scope, also known as a “telescopic sight,” is an indispensable tool for accurate shooting.
When I was a beginner, I didn’t really care to know about the inner workings of a scope, but I eventually learned to appreciate everything about it!
Understanding the scope and its functions may be difficult if you use it for the first time.
However, there’s no need to worry because I’m here to help! You won’t ask yourself, “How does a rifle scope work?” after reading my guide.
- Rifle Scopes at a Glance
- How Does a Rifle Scope Work?
- Best Riflescope Materials
- Are There Differences Between a Rifle Scope and Other Optical Devices?
- The Anatomy of a Rifle Scope
- Piecing It All Together
- Are Scopes Accurate?
Rifle Scopes at a Glance
Simply put, a rifle scope is a telescope that sits on top of your rifle. It’s an aluminum tube with a lens assembly or a collection of glass inside it.
Just like any other optical tool, scopes usually house the following components:
- Magnification lens: enlarge your target
- The reticle or fine lines: reference your target.
Scopes differ from iron sights, usually used in crossbows or machine guns. These tools are only good for focusing on a target, meaning they don’t offer magnification.
The rifle scope helps you see FARTHER than your naked eye because it is an optical tool.
Learning how it works can help you use your rifle more effectively.
How Does a Rifle Scope Work?
A rifle scope works by enlarging your target area so you can aim more accurately.
This is especially useful if you’re hunting or encountering fast-moving subjects, like running deer or flying birds.
Scopes use MAGNIFICATION to help you zoom in on your target. Basically, scopes are just a collection of lenses inside a tube.
However, the lens assembly, as well as the materials used, affects your scope’s optics.
That’s why it’s important to choose a scope that fits your needs, whether you’re a hunter or a sniper.
Best Riflescope Materials
Because you’ll attach your scope to a rifle, it must be nature-ready and protected against the elements.
That’s why most manufacturers choose AIRCRAFT ALUMINUM for a scope’s housing.
Aircraft-grade aluminum has two major advantages over other materials.
- Durability: it can withstand the elements
- Lightweight features: it doesn’t add extra weight to your rifle.
Some manufacturers make scopes using other materials, like durable titanium or steel construction. These can outlast dust, dirt, and rain.
The only disadvantage with these materials is they’re quite heavy to bring around.
For weather-proofing, a common tube scope would also use waterproof o rings for reinforcing joints.
I prefer scopes with this feature for all-around use, and I don’t have to worry about damage due to rain or snow.
The glasses are the most important part of your main tube.
Optic quality is one thing you should NOT skimp out on – and there are plenty of quality options even at lower price points.
I made the mistake of prioritizing other features over the glass. As a result, my images looked poor and blurry.
Don’t make the same mistake because you’ll lose out in the end! The best ones are multi-coated and protected from weather disturbances.
But why are coated materials better than uncoated glasses?
Coated optics are very good for maintaining the amount of light that makes it to your scope.
Uncoated optics reduce light transmission by 5%. More uncoated glasses inside your scope will transmit less light to you.
If you mostly hunt in darker conditions, coated materials are the best.
I recommend checking the materials to see if they’re also fog-proof and water-resistant.
If you wear glasses, you would know how annoying condensation buildup is. It is NOT something you want in your scope.
TIP: Choose fixed power scopes when possible. The optics are usually better than they would be with a variable power scope.
Are There Differences Between a Rifle Scope and Other Optical Devices?
A rifle scope isn’t too different from a camera, a microscope, or a telescope.
If you’ve ever encountered a DSLR or your science lab’s microscope before, it won’t be too difficult to wrap your head around a rifle scope.
Optical devices like cameras, telescopes, and rifle scopes are made the same way: a glass optic collects light and beams it to a focal plane.
Another piece of glass inside the lens assembly tube reorients the image to appear according to the angle you want.
The image passes through magnifying glasses. The light and color of that image transmit to your eyepiece, where you can finally look at it.
The Anatomy of a Rifle Scope
There are some specific differences with rifle scopes that you can’t find in other optical tools. A camera doesn’t have a reticle, for example.
Below, I’ll run you through the anatomy of a rifle scope so you can choose the one that’s right for you.
Scopes are optical devices, so it uses a series of lenses to improve your view of the target, much more than the human eye could give you.
Lenses are the most important part of scopes, and understanding how each lens works can help you figure out how all the knobs in your scope work.
Most optical devices work the same way: a lens close to the subject collects light and transmits it to the one closest to your eyes.
But what makes a rifle scope from a microscope or telescope is all the stuff in between.
I’ll walk you through the different lenses that make your rifle scope tick.
The basic anatomy of a scope will show three major sections:
- Objective bell
- Erector tube
Each section houses different lenses and adjustment knobs for various purposes.
Manufacturers often make scope housing with aircraft aluminum material for durability.
This material is best for housing since it’s lighter than traditional steel housing.
To help you with your own scope, I’ll move through the different parts of the scope, starting with your target, then toward your eyes.
The objective bell holds the objective lens in place.
It’s the largest and heaviest part of a scope, usually measuring around 40 or 50mm.
The objective lens gathers light from the object being observed and transmits the light to the ocular eyepiece. It’s usually the farthest piece from your eyes.
The objective lens is the most important glass in your set-up because it gathers light.
A poorer quality scope with a subpar objective may not be ideal in low-light conditions.
With a good-quality objective lens, you’ll be able to see more clearly and sight in your riflescope more accurately.
Take note that a LARGER objective lens gathers MORE light and results in a brighter image.
Modern rifle scopes almost exclusively use coated lenses to make their objective lenses. A coated objective lens glass does the following:
- Reduces light loss
- Improves image quality
- Retains vibrant colors from natural surroundings
I recommend purchasing a scope with a coated objective lens for the best shooting experience.
Coated lenses reduce reflection on your objective lenses; these days, they’re also scratch- and water-resistant.
Scope Tube/Erector Assembly/Erector Tube
The erector assembly contains all the improvements to make your riflescope easy to use.
It houses the reticle, erector lens, and magnification lens – all of which can help improve your target image.
The outer area of the erector tube contains several adjustment knobs, too. I’ll tell you all about how to adjust your scope in a bit.
The focus lens keeps your target image sharp by shifting its distance to and from the objective.
In ADJUSTABLE focus lenses, you can move the focus lens closer to the objective lens for distant targets and closer to the optical lens for closer targets.
In FIXED-FOCUS lenses, you don’t need to worry about the adjustment.
A fixed-focus scope has only one distance to focus from, so you don’t need to worry about adjusting for parallax.
You might need to adjust your position if your rifle has a fixed-focus lens scope to suit the distance of your rifle scope’s focus.
A reticle is a pattern of fine lines used to help keep stay on target. It centers your scope on your focal point or target so you can shoot more accurately.
Moreover, it determines the scale and position of your subject. I can’t imagine target shooting these days without it.
There are different types of reticles for different purposes.
You might have heard it referred to as “crosshairs” before, and that’s because the reticle is hair-thin in a cross pattern.
The most common reticle is the famed crosshair: just one vertical line down and one horizontal line across.
A dot sight or dot reticle is also pretty common: just one single dot in the center of your scope, with a concentric circle surrounding the dot.
There are more advanced designs, like mil-dot reticles, duplex reticles, or German reticles.
There are even reticle designs that are illuminated or Christmas tree-shaped!
What Should You Use If You’re Starting Out?
A crosshair will be just fine for most purposes.
Traditionally, manufacturers used tungsten wires for a reticle. But these days, an etched reticle is more common.
Erector Lens Assembly
To correct this, the erector lens flips the image so that the image right-side up arrives at your scope’s ocular lens.
Without the erector lens assembly, you would be shooting upside-down images! That’s why an erector is important.
Like the other glasses I discussed, coated options are best for reducing light loss.
The magnification lens is usually only found in a variable power or a magnification scope.
The magnification works a lot like a DSLR zoom camera if you’ve ever seen one before.
Here’s what happens if you adjust the power dial to the following settings:
- Maximum power: moves magnification optics towards the objective optics
- Lowest power setting: moves the magnification glass towards the ocular lens, nearer your eye.
It refers to that part of your scope where your image is at its SHARPEST and is parallel to your eyes.
In a scope, there are two focal planes where your target is at its sharpest.
But when manufacturers refer to “focal plane,” they usually mean where the reticle is printed.
The erector lens assembly may differ between manufacturers.
- First focal plane scope: the reticle is in front of the magnification, closer to the objective optic.
- Second focal plane reticle: located behind the magnification lens, nearer your eye.
The reticle in a riflescope with an FFP will increase or decrease in size depending on the magnification settings in a variable power scope.
Meanwhile, an SFP plane reticle stays the same size regardless of the setting of your variable power scopes.
You can learn more about focal planes in my FFP and SFP Beginner’s Guide.
What setup should you use?
If you’re a hunter in the United States, you might be more used to the SFP setup.
That’s because the ease of using a non-moving/changing reticle is more convenient to handle.
Long-distance shooters prefer a first focal plane reticle because of the precision work they can explore with these types.
Your choice of plane scopes depends on your preference, and you can still achieve excellent shooting accuracy with either set-up.
However, here are the following plane scopes I recommend depending on your shooting needs:
- FFP rifle scopes: long-distance shooting
- SFP rifle scopes: regular hunting.
The eyepiece assembly, which contains the ocular lens, is the scope section closest to your eye. The final destination of your image is the eyepiece area.
The ocular lens is where the light from your objective lens is directed. It’s the focal closest to your eye when you’re looking through an optical device.
Ocular lens quality is important because an easily breakable material can injure your eye.
Coated ocular lens options also reduce fog from your view.
Rifle Math: Settings Your Sights Effectively
Reading a Rifle Scope’s Numbers
When I was a beginner, there were so many numbers in the product names that it was really confusing.
But it’s fairly simple!
The number or numbers BEFORE the “x” show the magnifying power of your scope, while the number AFTER the “x” is the diameter of your optical lens.
For example, a 3-9×40 scope means that your scope has a magnification range of 3-9x and an objective lens diameter of 40mm.
A 4×32 scope has a 4x magnification and a 32mm diameter.
Magnification and Power
If you’ve used a DSLR or smartphone camera before, you already have a head-start.
A scope’s magnification works a lot like any camera’s zoom lens.
Zooming in and out enlarges your subject from where you’re standing. The terms for zoom and magnification are just about the same.
The unit of measure for magnification is power.
A lens’ magnifying power, or magnification range, shows how large the image can appear.
Relationship of Camera Setting to the Image’s Largeness
- 2X: the subject is twice as large
- 4X: the subject is 4 times as large
- 16X: the subject is 16 times as large
Rifle scopes have larger magnifications, of course. Some rifle scopes even go as long as 80x magnification.
Fixed Power vs. Variable Power Scopes
A fixed-power scope is only available in ONE zoom setting, such as 4x.
Meanwhile, a variable power rifle scope offers a range of power settings to choose from, such as 3-9x magnification.
You can change the zoom in a variable scope by turning the power ring dial a few notches until you arrive at your desired power.
You can find the power ring in the erector tube of most scopes.
A fixed-power scope is lighter and more affordable, especially for beginners.
While it’s not as versatile as a 3-9x scope, the lenses are better quality than zoom magnification.
However, I recommend a variable rifle scope if you need to shoot from various distances.
Learn more about my in-depth comparison guide on fixed and variable power scopes!
Which Magnification to Use?
You won’t need a rifle scope with that much enlargement for most hunting purposes.
In fact, I recommend getting a scope with fixed power with just one magnification, like a 4x scope.
Your choice of amplification depends on your terrain and your weapon of choice. Rifles have different requirements from shotguns and handguns.
I recommend a scope that can magnify to 300 yards for deer hunters.
Target shooters could use more magnification fit for an accurate shot at 1000 yards.
For those who want versatility, getting scopes with red dots on top is also something to consider.
Remember that parallax errors often happen with higher magnifications, so you may need to make more parallax adjustments (I’ll teach you how to do that below!).
Objective Lens Diameter
The objective bell, along with the objective lens, is the largest part of your scope.
It makes sense that manufacturers measure scopes using the objective lens diameter.
While it may tempt you to choose a large objective bell for larger lenses, it’s difficult to mount on your rifle.
Large objective bells are also heavy, so if you move around in the middle of a hunting game, smaller 40mm lenses might be a better choice.
Sometimes, conditions aren’t ideal. I had to resort to uncomfortable body positions to put my prey in focus.
Fortunately, most basic riflescopes feature adjustment knobs for fine-tuning your target acquisition.
Windage, elevation, and parallax adjustments can make deer hunting easier for you.
These knobs are located between the objective bell and the eyepiece in the main erector tube area.
Windage compensates for the differences in horizontal travel of your bullet. Different factors, like wind, can drift your bullet sideways.
Windage adjustments help by adjusting your bullet from left to right so that you can adjust for horizontal deviations from the point of impact.
The windage adjustment turret is on top of your scope.
Moving the dial left or right can help adjust your point of impact from left to right.
What goes up must come down.
Bullets travel in a projectile, so you usually have to point your rifle higher to hit a more distant target.
Fortunately, gone are the days when you had to aim your rifle high or low to compensate for the vertical projectile drop of your bullet.
With elevation adjustments, you can fine-tune the vertical deviations of your bullet to hit the point of impact more effectively.
Just remember that the elevation adjustment is the opposite of what you’d expect.
- The low point of impact: move your riflescope’s direction upward (COUNTERCLOCKWISE)
- The high point of impact: move your scope downward (CLOCKWISE)
Because the adjustments are so minute, the dials turn in clicks. There are two types of click values in the market:
- Milliradians (MRAD): changes the impact point by 0.26 inches
- Minute of Angle (MOA): changes the impact point by 1/4 of an inch.
These two values are just different measurement units, like centimeters vs. inches.
The numbers are close together, and choosing one or the other depends on your preferred measurement method.
If you think in feet and inches, MOA might suit you.
Parallax is the displacement of the object depending on your perspective or point of view.
In a riflescope, parallax error shows up as a misaligned reticle – so you see grid-like, multiple reticle patterns reflected in your view.
It’s an optical illusion that can make your target look out of focus even when it isn’t.
You might notice that the reticle is no longer in your target position when you move your head a bit to the side.
That’s a parallax error that you’ll need to adjust for.
A basic riflescope offers a parallax adjustment. Here’s what you should do to adjust the parallax:
- Turn your parallax knob as you move your gaze slightly sideways.
- Keep adjusting until the reticle appears fixed where your target is.
Field of View
The field of view is how wide you can see, given a particular distance.
If you’ve used a camera before, you’d know that zooming into a subject narrows the width of your vision.
Here’s how to illustrate the field of view:
- Look at a horizon with your naked eye.
- Then, look through a camera or your scope at any subject in the middle.
You lose a lot of width around the subject when you inch closer to your subject with your camera or scope’s field of view.
It’s important to note your field of view, especially if you usually target moving subjects during your shooting game.
You might need a LARGER FOV (and, therefore, a lower-powered lens) if you’re a deer hunter.
If you’re a target shooter, FOV is less important than power.
It’s all about balancing your FOV with your lens power to suit your needs and how well you can see with your naked eye.
Exit Pupil Diameter
The exit pupil diameter is the width of your exit pupil.
The actual width of the light that actually reaches your optical lens and is available for your eye to see.
The Exit Pupil Diameter of the Human Eye Based on Light Conditions
- 2-3 mm: Bright light conditions
- 7 mm: Low light conditions
It is tempting to get a larger target through a larger exit pupil diameter, but you need to remember that our eyes can only take so much.
A good middle ground of around 5-6mm exit pupil diameter is best for versatility.
But how would you know if your exit pupil diameter fits your needs?
Simple. Just divide your objective lens diameter by your scope’s magnification to solve for the exit pupil.
Take a 4-16×50 scope, for example.
- 50 ÷ 4 = 12.5mm
- 50 ÷ 16 = 3.125mm
Eye relief is the distance from your eye to the ocular lens.
I’ve been talking about how cameras are like scopes since they’re both lens-operated optical devices.
But the similarities between cameras and scopes end there.
However, with cameras, you can keep your eye super close to the eyepiece. It’s a different story with scopes.
There are two reasons eye relief is so important.
First, having your eye too close to the scope narrows your FOV. You can’t see the entire target collected in your optical lens if you’re too close.
In fact, your eyesight could become quite fuzzy.
Second, rifle scopes are attached to your rifles, meaning it’s prone to something that cameras will never be: recoil.
If your rifle has a larger recoil, you could injure your eye if you stick it too close to the eyepiece. Keeping your distance is essential!
For variable power scopes, add 3 inches increase in eye relief with a decrease in power.
A larger magnification range calls for less eye relief, but always remember that your rifle can recoil!
It’s also VITAL that your scope is attached correctly and has the correct scope height for you.
Piecing It All Together
So how does a rifle scope work? How do you use one?
I’ll walk you through using a scope, so you won’t have a hard time using your rifle scope when you try it out for the first time.
Point your rifle at a target and look through your scope. Remember the eye relief!
Make sure that the entire exit pupil is in view.
Direct your riflescope toward a non-moving target. Focus on the target and make sure to KEEP IT ALIGNED with the reticle.
Now shift your head from left to right to check for parallax.
Adjust the parallax adjustment dial until you see that it no longer shifts as you move slightly from different points of view.
If your target is lower, you can adjust your elevation higher by turning the knob a few clicks until you can imagine that the bullet will hit your target perfectly.
If it’s a windy day, you might also need to experiment with your windage adjustment, taking note to turn the turret in clicks.
If the fixed image remains clear and centered in your scope, then your scope is READY TO USE in the great outdoors.
Are Scopes Accurate?
Scopes are used to make a shooter’s target larger and clearer, but the overall accuracy still depends on the firearm and the user’s skill level.
I would only call a scope “accurate” if all the components are functioning properly, which would result in landing precise, on-the-dot shots.
Accuracy is dependent on several factors, such as weather, proper use of features, ammunition, mounting, etc.
There are plenty of riflescopes in the market, so you might get confused by the options if you’re only starting out.
But I hope my crash course can help you get started with all the tools you need for better hunting!
I know missing your targets on the first few tries can be frustrating, but do not give up!
Keep practicing, and eventually, you will be shooting like a pro!
FINAL TIP: For more information about riflescopes, you can read up on my Guide on the Different Scope Mounts to help you cover all the bases.