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How Does a Rifle Scope Work? — Beginner’s Basic Guide

How Does a Rifle Scope Work

A rifle scope, also known as a “telescopic sight,” is an indispensable tool for accurate shooting.

Trying to understand the scope and its functions may be difficult if you’re using it for the first time.  

However, there’s no need to worry because we’re here to help!

You won’t be asking yourself, “How does a rifle scope work?” once you’ve finished reading our guide.

Rifle Scopes at a Glance

At a Glance

Riflescopes aren’t so difficult to explain. Simply put, it 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, which are usually used in crossbows or some 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 would 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 to 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.

History of the Rifle Scope

History

The scope hasn’t been around forever. In fact, scopes are relatively new inventions, dating back to the late 19th century.

A book published in 1844 called the Improved American Rifle documents some of the first rifle markers manufactured in New York.

These aren’t like the scopes we have today, though. The idea of using a telescope tube came in 10 years later. Willian Malcolm, a New York manufacturer, introduced optics to lenses.

It was during the World War when rifle scopes saw big improvements. With trench warfare came the rise of the snipers.

Back then, 6x magnification was considered a feat. But with today’s technology, we could use even 10x magnification scopes with hunting rifles.

Best Riflescope Materials

Body/Housing 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. We prefer scopes with this feature for all-around use.

Lens Materials

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.

Don’t make the mistake of prioritizing features over the material because you’ll lose out in the end.

The best ones are coated and protected from weather disturbances.

Why are Coated Materials Better vs. 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.

Why Should You Always Check Check on Your Materials?

We recommend checking the materials to see if they’re also fog-proof and water-resistant.

We all know what it’s like when condensation builds up in our eyeglasses. That’s 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, then 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 so that it appears 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

Anatomy

There are some specific differences with rifle scopes that you can’t find in other optical tools, though. A camera doesn’t have a reticle, for example.

Below, we’ll run you through the anatomy of a rifle scope so you can choose the one that’s right for you.

Optics

  • 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. We’ll walk you through the different lenses that make your rifle scope tick.

Scope Sections

The basic anatomy of a scope will show three major sections: 

  • Objective bell
  • Erector tube
  • Eyepiece

Each section houses different lenses, as well as adjustment knobs for various purposes.

Manufacturers often make scope housing with aircraft aluminum material for durability. This is the best material for housing since it’s lighter than traditional steel housing.

To help you with your own scope, we’ll move through the different parts of the scope, starting with your target, then towards your eyes.

Objective Bell

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.

Objective Lens

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.

Modern scope manufacturers almost exclusively use coated lenses to make their objective lens. A coated objective lens glass does the following:

  • Reduces light loss
  • Improves image quality
  • Retains vibrant colors from natural surroundings

We recommend purchasing a scope with a coated objective lens for the best shooting experience. Coated lenses reduce reflection on your objective lense, and these days, they’re also scratch-resistant 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. We’ll tell you all about how to adjust your scope in a bit.

Focus Lens

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.

Reticle

A reticle is a pattern of fine lines used to help keep you on target. It centers your scope on your focal point or target so you can shoot more accurately.

A reticle determines the scale and position of your subject. It would be hard to imagine target shooting these days without it.

Cross Hairs

You might have heard it referred to as “cross hairs” before, and that’s because the reticle is hair-thin, in a cross pattern.

The most common reticle is the famed cross hair: just one vertical line down and one horizontal line across.

Dot Reticle

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 reticle, duplex reticle, 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 cross hair 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

Objective lenses produce inverted images because of the curvature. To correct this, the erector lens flips the image so that what arrives at your scope’s ocular lens is the image, right-side up.

Without the erector lens assembly, you would be shooting at upside-down images. That’s why an erector is important.

Just like the other glasses we talked about, coated options are best for reducing light loss.

Magnification Lenses

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 lenses, nearer your eye.

Focal Plane

Focal Plane

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 our 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 set-up. 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 we recommend depending on your shooting needs:

  • FFP rifle scopes: long-distance shooting
  • SFP rifle scopes: regular hunting.

Eyepiece

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.

Ocular Lens

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

Rifle Math

Reading a Rifle Scope’s Numbers

When you buy a scope, you might see numbers like 3-9×40 or 4×32. What do these numbers mean?

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.

So a 3-9×40 scope means that your scope has an enlargement 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’s 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 magnification, 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. 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. Turning the power ring will move your rifle scope’s magnifying optics towards or away from the objective optics.
  • A scope with fixed power is lighter and more affordable, especially for beginners. While it’s not as versatile as a 3-9x scope, the lenses are of better quality than zoom magnification.

However, if you need to shoot from various distances, we recommend a variable rifle scope.

Which Magnification to Use?

For most hunting purposes, you won’t need a rifle scope with that much enlargement. In fact, we recommend getting a scope with fixed power with just one magnification, like a 4x scope.

Your choice of amplification depends on the terrain you’re in and your weapon of choice. Rifles have different requirements from shotguns and handguns.

We 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 error tends to happen more often with higher magnifications, so you may need to make more parallax adjustments (we’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. So 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.

Adjustment Controls

Adjustment Controls

Sometimes, conditions aren’t ideal, and you might need to adopt uncomfortable body positions to put your 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 in the main erector tube area, just between the objective bell and the eyepiece.

Windage Adjustment

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.

Elevation Adjustments

Elevation Adjustments

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 have 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.

  • Low point of impact: move your riflescope’s direction upward (COUNTERCLOCKWISE)
  • High point of impact: move your scope downward (CLOCKWISE)
Elevation Adjustment Values

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 really just different units of measurement, like centimeters vs. inches.

The numbers are close together, and choosing one or the other really depends on your preferred method of measurement. If you think in feet and inches, MOA might suit you.

Parallax Adjustment

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 could 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.

If you’re a deer hunter, you might need a larger FOV (and therefore, a lower-powered lens). 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 – meaning the actual width of the light that actually reaches your optical lens and 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.

For instance, in a 4-16×50 scope, the objective lens’ diameter at 4x power is 12.5mm, and at 16x, giving you an exit pupil diameter of 3.125mm.

Eye Relief

Eye Relief

Eye relief is the distance from your eye to the ocular lens. Now, we’ve been talking about how cameras are like scopes since they’re both lens-operated optical devices.

But the similarities of cameras and scopes end there. Eye relief is important when using a scope; you can’t just stick your eye into the eyepiece and expect to hit your target accurately.

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. So keeping your distance is essential.

For variable power scopes, just 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?

We’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.

How an Image Travels Through a Scope

  1. Point your rifle at a target and look through your scope. Remember the eye relief! You don’t want to hurt your eye with your rifle’s recoil.
  2. Make sure that the entire exit pupil is in view. Direct your riflescope towards a non-moving target. Focus on the target and make sure to KEEP IT ALIGNED with the reticle.
  3. 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.
  4. 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 need to experiment with your windage adjustment as well, 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.

Conclusion

Conclusion

There are plenty of riflescopes in the market, so you might get confused by the options if you’re only starting out.

But we hope our crash course can help you get started with all the tools you need for better hunting!

So, what are you waiting for? Go ahead and use your rifle scope!

FINAL TIP: For more information about riflescopes, you can read up on our Guide on the Different Scope Mounts to help you cover all the bases.

 

CHANGELOG:

September 22, 2021 - Reviewed and updated article links

About the author

Christopher Wade

Christopher Wade is a true outdoorsman. After spending most of his career as a firearms expert and instructor in Nebraska, he retreated to the great outdoors to enjoy retirement.

Christopher’s expertise in handling firearms and hunting gear are what propelled him to create the Shooting Mystery blog. He hopes for all readers to gain useful and practical knowledge for enjoying their time outdoors.