Rifle Scopes Explained: A Beginner’s Guide

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By Dennis Howard •  20 min read

Start a discussion with another hunter or a target shooter, and soon it will turn to rifle scopes and optics.

Among the ongoing topics with most shooting enthusiasts, rifle scopes are probably one of the most popular and heavily debated issues. Unfortunately, many of the most ardent arguments are based on an incorrect or incomplete understanding of how rifle scopes work, their designs, and the proper relationship between a rifle and scope choice.

In technical terms, a rifle scope is a telescopic optical device similar to a refracting telescope equipped with a reticle which is used as a referencing point for aiming and, in some cases, range estimation.

Most telescopic rifle sights use a series of glass lenses mounted in an erector structure that allows the lenses to be moved to facilitate changing the magnification of the image and sharpening the focus.

A telescopic rifle scope sounds simple. However, even the simplest fixed magnification scopes require precise alignment and the best possible materials to provide an image suitable for accurate distance shooting. Many variables can affect the quality of a rifle scope and features that further enhance the usefulness of rifle scopes.

Understanding how the basic functions of a rifle scope interact with these features is an important part of making the best rifle scope choice for your gun.

The Basics of a Rifle Scope – Putting the Parts Together

Most shooters know the terminology of rifle scopes well enough, but few really understand the physical parts that are described by those terms.

We easily toss around words like parallax, windage, elevation, lens coatings, and diopter. Yet, if asked to define and explain those terms and how they work in a rifle scope, few shooters understand.

Let’s lift the veil on the basic parts of a rifle scope and get inside the terminology.

The Heart of A Rifle Scope – The Lenses

At the very foundation of any optical telescopic rifle sight are the lenses that gather, focus, magnify, and transmit the light that makes up the image we see through the scope.

If there is one truth about rifle scopes, it is that the quality of the glass is critical to the quality of the scope. You can design and manufacture the highest quality scope in the world, but if the glass used in the lenses is sub-par, the entire scope will never perform adequately.

Let’s Shed Some Light on Glass

We are all familiar with glass and glass lenses. From the windshield of our cars to our eyeglasses, we peer through glass of some sort many times a day. However, the glass used for windshields and the windows in your home is a far cry from the glass used to make the lenses in your rifle scope.

To make a quality glass lens for a rifle scope, many variables must be controlled. The technology to produce the glass and cut, grind, and polish the lenses can be incredibly expensive.

The Trinity of Quality Optical Glass

Most optical glass is judged using three criteria, Clarity, Brightness, and Color.


Clarity refers to how clear the glass is and how well it transmits light without distortion. The optical glass must be as free as possible from any contaminants, distortions in the glass, and bubbles. Any of these found in a piece of optical glass can make it unusable for rifle scope lenses.


Brightness is a term often misunderstood by hunters and shooters.

Brightness has nothing to do with a piece of optical glass and its ability to gather light.

Brightness refers to the amount of light lost between the glass’s front and back as the light passes through. Brightness and clarity are closely associated since impurities affect optical glass’s ability to transmit and refract light.


The highest quality optical glass transmits light without imparting any noticeable color changes to the image.

This is most notable in low-quality rifle scopes. If you look through a rifle scope and notice that the images pick up a slight blue or orange tinge, you have experienced a color shift in the glass. High-quality glass transmits light without adding any perceptible color to the images.

Inside the Tube – Getting the Image to Your Eye

Even the simplest fixed magnification rifle scope is more than a couple of lenses.

Inside the tube of the telescopic sight is a complex arrangement of lenses that work together to give you the proper image in the right relation to your eye and in focus.

In truth, a rifle scope is a system with multiple lenses, each with a specific purpose.

The Objective Lens and the focal point

The objective lens assembly is placed at the furthest point on your rifle scope from your eye. At this point, the light transmitted from your target enters the rifle scope and begins the trip to your eye. The objective lens bends the light slightly, causing it to focus on a point inside the rifle scope.

When you hear people talk about the first focal point, this is the place to which they are referring.

First Focal Plane Reticles

If your rifle scope is designed as a first focal plane reticle, it is at this point in the light’s trip down the scope tube that the reticle image is injected into the image.

A first focal plane reticle is in front of the magnification lens assembly, which means that as the image is magnified, the reticle image is also magnified and keeps its size relative to your target.

Getting the Image Right – The Erector or Reversal Lens Assembly

As the light passes through the first focal point, it is turned upside down relative to your eye.

To keep things properly oriented, the light must now pass through the erector or image reversal lens assembly to turn the image back to the proper orientation. This lens assembly is usually several lenses that work together to transmit the light without distortion.

Making the Target Easier to See – Magnification

Once properly positioned, the image passes through the magnification lens assembly. On some fixed power scopes, this is a simple lens arrangement that is fixed inside the scope tube.

On variable magnification range scopes, this lens assembly moves to increase or decrease the magnification range of the image. As you turn the magnification ring on your scope, the magnification lens assembly moves forward and backward in the scope tube to change the size of your image.

The Second Focal Plane – Another Reticle Point

By its nature, the erector assembly refracts the light to reorient the image, meaning the light must pass through a second focal point, normally referred to as the second focal plane.

Here, many scopes place the reticle rather than putting it at the first focal plane. If your scope has the reticle in the second focal plane, the reticle image is injected into the system at this point.

Because the reticle image is inserted after the magnification lens assembly, the reticle image doesn’t maintain its size in relation to the target image.

The Ocular Lens Assembly – Getting the Image to Your Eye

At the end of the scope nearest to you and furthest from the objective lens is the ocular lens assembly.

Here, the scope gathers the light that has been transmitted through the system and prepares it for your eye. If your scope is equipped with an adjustable diopter, it will be part of the ocular lens assembly.

Eye Relief

Here we must stop to talk about eye relief. Eye relief is not, technically speaking, part of the inner workings of your rifle scope. It is, however, a function of the ocular lens assembly and an important consideration when choosing a scope.

Eye relief refers to the distance your eye must be from the ocular lens to see the full field of view in the scope. Eye relief varies from scope to scope depending on the type of rifle it is mounted and the shooter’s preferences. We will speak more about eye relief later in the article.

Rifle Scope Construction – Compromises in Strength and Weight

This brings us to the parts of your rifle scope that you can see, touch, and manipulate.

Scope construction is an engineering dilemma in many ways. The scope must be constructed so that it is rigid and durable. Rifle scopes, by and large, take a lot of abuse from weather, terrain conditions, and shooters. It would be easy to build a scope that would survive any conditions, but the result would be so heavy it would be almost impossible to use on a hunting rifle.

On the other hand, eliminating weight is also an easy task by choosing less durable lightweight materials, thinner metals, and less well-engineered components. The result would certainly be lighter but also prone to damage or fail to be as accurate as many shooters require.

In the end, scope designers and engineers face making compromises that keep the scope’s weight to a manageable level while also providing the durability and ruggedness needed without pushing the cost of the scope well above what most shooters can afford.

The Scope Tube

The main structural part of any rifle scope is the scope tube.

The scope tube holds the working parts of the internal scope components, provides support for the ocular and objective lens assemblies, houses the windage and elevation adjustments, and is where the scope mounts support the scope on your rifle.

Scope Tube Diameter

Typically scope tubes are standardized to 1-inch, 30-mm, and 34-mm diameters. When you consider the complexity of the workings that must fit inside a scope tube, it is amazing that these small-diameter tubes can do the job.

Scope rings are made for these standard diameters to facilitate easy mounting that is solid without damaging the scope when they are properly installed.

In general, the most common diameters of scope tubes are 30 mm and 1-inch. 34-mm tube scopes are more expensive and designed for specialty scopes and shooting activities. Neither size of the scope tube has an advantage over the other.

Windage and Elevation Turrets

The housing that supports the windage and elevation turrets is in the middle of the scope tube. These knobs are used to adjust the lenses of the erector or elevator system to correct the aim of your scope reticle in relation to the target.

The top knob, or turret, adjusts the elevation of the impact point of your scope by moving the erector assembly up or down in the appropriate direction.

Likewise, as you are looking through the ocular lens, the turret on the right side of the scope adjusts the reticle’s windage right or left as needed.

Turrets are graduated in clicks that allow you to make precise windage and elevation adjustments while shooting. The graduation of the adjustments is measured in mil dot increments or MOA increments.

Parallax Adjustment – Keeping Things in the Same Focal Plane

Some scopes feature adjustable parallax. Parallax occurs when the image of your target and the image of the reticle in your scope is not on the same focal plane. At great distances, this can be a problem, and some more expensive variable power scope models have adjustable objective lens assemblies that can eliminate parallax errors in your scope.

Ring or Knob Parallax Adjustment

Some scopes, particularly those with second focal plane reticles, also offer parallax adjustment. Typically, first focal plane scopes have parallax adjustments that move the objective lens assembly to correct parallax error.

This is usually an adjustment ring on the objective end of the rifle scope.

The other method of parallax adjustment is done by putting a third knob or turret on the left side of the scope to adjust the reticle and correct parallax errors. On many scopes with this type of parallax adjustment system, the third turret also allows you to control features such as lighted reticles, reticle color, or range-finding features.

Magnification Ring – Getting Up Close

Between the ocular lens system and the erector is the magnification system.

Most variable power scopes manage the magnification range settings using a ring that can be turned to increase or decrease the magnification. Most hunting scopes that feature variable power use this type of system.

Some target shooting variable power scope magnification rings may be fitted with levers or posts to facilitate easier adjustments to the magnification system.

Diopter Adjustments

If you are bound to a pair of glasses like I am, then you may find that a scope with a diopter adjustment makes life easier. Basically, a diopter adjustment on your scope allows you to dial in the proper adjustment so that you can use your scope without needing your glasses.

Wearing glasses and using a rifle scope can sometimes be very inconvenient. Glasses can fog or become rain splattered. Glare on your eyeglasses may make the image in your scope difficult to see. Adjusting the ocular lens focuses to eliminate the need to wear your eyeglasses can make your shooting life much easier.

Reticles – The Art of Aim

One last piece of the rifle scope puzzle to be considered is reticles.

There are almost as many styles and types of reticles as there are scopes. These choices range from the basic and classic crosshair reticle to sophisticated and often complicated reticles that can be used to perform range-finding and windage estimation.

Choosing a reticle is a very personal decision driven by your needs, expectations, and uses of your rifle and scope.

Personally, I prefer to keep the reticle in my scope as simple as possible. I prefer working with a scope graduated in MOA instead of mil dot markings. For me, it is easier to remember that one MOA at 100 yards is 1 inch.

Picking A Rifle Scope – Understanding Your Needs and Expectations

When I start shopping for a new rifle scope, as much as I am interested in the features, bells, and whistles, I always start by considering some basic criteria that help me understand what I need from a scope.

Different rifles, different uses, and different expectations can majorly determine which scope is best for a given situation.

Here are a few things to keep in mind when searching for the perfect rifle scope:

What Rifle Am I going to Scope?

This may seem like a very simplistic question, but it is a determining factor in which scopes I consider as I shop.

If I put a scope on a Ruger 10/22, I will probably limit my choices to rimfire scopes. If I want to put a new scope on an AR-15 that I use for both target and hunting, there is another set of variables to consider. When it comes to purchasing dangerous game scopes for big-bore rifles, a completely different set of criteria come into play.

Your rifle scope should be matched closely to the rifle and caliber onto which it will be mounted. I see far too many people with more scope on their rifles than they need, which can cause its own set of problems.

Over-scoping a rifle often causes more frustration than a rifle that is under-scoped for the uses to which it is put.

How Do I Intend to Use My New Scope?

Are you a hunter or engaging in serious target shooting or competitions? Even the type of competition should be a consideration.

How you intend to use your scope can affect magnification, objective lens size, and eye relief decisions. This is all in addition to budget considerations that we all face. You need to clearly understand how you will use your scope before you start shopping.

Do You Need More Magnification?

High-magnification scopes are a wonder to use and shoot if you know what you are doing. Long-range shooting often calls for more magnification than traditional hunting. Most hunts in North America are performed at ranges 250 yards or less. A good scope with fixed power is often all that is needed for this kind of hunting.

As distances increase, it is customary for magnification increases as well. However, an experienced shooter can often compensate for a lack of magnification on the rare occasion that they go beyond their customary distances.

Higher magnification brings its own set of problems and issues. With higher magnification, you often get more sensitivity to scope movement, parallax errors, and issues with light transmission, clarity, and color.

Fixed Vs. Variable Power Scopes

In many cases, I prefer a good fixed power scope over a variable scope. Variable scopes are more complicated and have more failure points. A variable scope is usually more expensive than a fixed power scope.

Putting the difference in cost to a higher quality fixed power scope is often a better choice.

I prefer putting money into good scopes rather than lots of bells and whistles that I may never need or use. Even for long-range shooting, often, a fixed power scope is effective.

More important to me is getting more light through the scope with higher clarity and a sharp sight picture. However, your preferences may be different than mine.

Budget Considerations

Before I even start looking at catalogs online or in the stores for a new scope, I set myself a budget.

It is all too easy to get caught up in the moment, especially when dealing with a salesperson or an online ad designed to entice you into a purchase. You should know your upper limit for a scope purchase before you begin the process. This will help you narrow your options, focus on finding the critical factors in your decision, and make the best decision about features vs. cost.

Critical Factors in a Scope Decision

Once you have thought about the above factors and made those basic decisions, it is time to start shopping for a new scope. Now it is time to consider those critical factors about the scope you purchase.

Here are some criteria that I use about any scope purchase that I think you should consider as well:

Optical Glass Quality

The quality of the glass in your new rifle scope is the very foundation of how well the scope will perform and how satisfied you will be with your decision.

The best craftsmanship and design cannot make poor optical glass perform properly.

Source and Manufacturing

For the best optical glass, Europe is still the number one choice. Scope makers who source their optical glass from Europe tend to have the best quality lenses. However, technology is closing the gap in lens quality in many ways. The optical glass from Japan and the Philippines is rapidly approaching the glass from Europe.

A lot of rifle scopes are now coming out of China. It has been my experience that the optical glass used in most of these Chinese-manufactured scopes is on the mediocre side. Occasionally you will get some fair to good glass from China, but on the whole, the quality control of the glass production and the grinding is sub-par.

Unfortunately, determining the source of the optical glass used by some manufacturers is difficult.

On the whole, reputable scope manufacturers will be forthcoming about the source of their optical glass and lenses and where the scopes are manufactured and assembled.

Coated Lenses

Lens coatings are a minefield when shopping for a new optic. Most scope manufacturers use a proprietary lens coating system, and it can be hard to substantiate their claims. I advise dealing with reputable and well-known scope manufacturers with a proven track record.

That said, getting the best coated lenses on your scope is well worth the effort and money.

Lens coatings can enhance the quality of the sight picture in your scope by bringing more light transmission through the scope and protecting the lens of your scope from moisture, dust, debris and mechanical damage. Most scopes have lenses that are exposed to air coated in multiple layers.

Higher-quality scopes will coat and protect even the internal glass components.

Objective Lens Diameter

Objective lens diameter is important depending on how, when and where you hunt or shoot.

In general, the larger the objective lens diameter, the more available light is transmitted through the scope. In addition, the light passing through the scope yields a wider field of view to your eye. A larger lens is especially useful as magnification increases in long-range situations.

Unfortunately, large-diameter objective lenses add bulk to a scope as well as weight. These large lenses also require a longer focal length translating into a longer scope tube. \

At close range, a large diameter scope may make target acquisition difficult, if not impossible.

Adding the Bells and Whistles

Once you have the basic criteria for your new scope, you can begin to think about which of the accessory features you would like to have on your scope. There are some bells and whistles that can make a quality scope outstanding. Some can take away from the usefulness of a scope under certain circumstances.

Judging which additional features you want on your scope is a purely personal choice.

Illuminated Reticles

Perhaps the hottest innovation in rifle scopes recently is illuminated reticles. Even many of the more expensive scope manufacturers now offer a high-end scope with an internally illuminated reticle.

There are advantages to reticle illumination that should be considered:

There are some downsides to adding illumination to a scope.

I must admit that I like an illuminated reticle and have come to prefer having this feature on my scopes.

Bullet Drop Compensator

Many new scopes are built with a drop compensator. These ballistic compensators are typically designed for a specific bullet weight and load, and you must make manual adjustments if you shoot a different cartridge.

However, some more sophisticated scopes offer systems that allow you to input various variables, including a ballistic coefficient, as well as load data to customize the drop compensation system.

This can be a very attractive feature if you are a serious competitive target shooter or long-distance hunter.

Range Estimation

There are several options for range estimation as a rifle scope option. Some rifle scopes now come equipped with laser rangefinder capabilities that can do precise distance calculations out to several thousand yards. Using MOA or mil dot scope reticles with range estimation markings is another method that can be employed.

For long-range shooters and competitive target shooters, range estimation with your rifle scope can be a great addition.

Understanding Rifle Scopes Before you Make Your Purchase

You may be varmint hunting or just shopping for shotgun and muzzleloader scopes. In any case, understanding the ins and outs of rifle scopes is an important part of making a wise decision about purchasing a new scope.

Most scopes have the same basic features and parts and look much alike to the naked eye.

Don’t let your shooter’s eye lead you astray. Learn what to look for and how to shop for your rifle’s best possible scope choice.

Dennis Howard

A life long hunter, fisherman, and outdoorsman, after surviving a devastating tornado in his home town, he saw the effects on people's lives as they struggled to cope. He built his first bugout bag a few weeks later and has been a dedicated prepper/survivalist since that time. After a career as a fireman, Dennis opened a retail store (FFL approved) catering to the military, law enforcement, and like-minded individuals. The store built their own AR platforms. Furthermore, Dennis was also an NRA instructor in both long gun and handgun as well as a certified range safety officer. Read his full interview here.