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Have you ever wondered what goes on inside a rifle scope? A rifle scope is a sighting device made up of many parts and components, all working together for the same end result. This optical device has both external and internal components that ensure its functionality. In this article, we will look at the major components and systems that make up a rifle’s scope internal anatomy. Here’s what is going on in your scope!

How Does A Scope Work

A scope’s primary function is straightforward: it assists the shooter in aligning the barrel of a weapon with the target. However, the way a scope does this is a little more complicated. Although the external components have their own use, but the internal components are the most important aspect of a scope, and they help you to understand better how a high-tech optic functions.

A rifle scope’s interior works similarly to a telescope. There is a bigger objective lens at the front of the scope where light enters it, and an ocular lens at the back that focuses the transmitted light on the eye of the shooter. For the full length of a riflescope, you have the ocular lens, magnification lens, focus lens and objective lens.

Internal Anatomy of a Riflescope

A scope’s internal anatomy is a little bit complex, and it is divided into four main sections:

Objective lens assembly, focus lens assembly, erector lens assembly and Ocular lens assembly.

Objective Lens Assembly

If you look around, you will find out that all the lenses found in most of the contemporary rifle scopes currently available in the market are coated to prevent reflection or glare. The lesser the amount of light that is reflected by the lens of a scope, the higher the amount of light that will be transmitted to the eye of the shooter. Coated lenses may significantly improve a scope’s light-collecting capabilities, boosting its usability in low-light shooting applications. 

Why did we have to first mention lens coatings? We talked about lens coatings first because the objective lens of a scope is the primary light-collecting lens; its diameter and coating may make or break the scope’s low-light capabilities. 

The objective lens assembly is responsible for housing the objective lens in the tube of the scope. If you have an AO scope, you may be able to compensate for parallax by tuning the adjustable objective and adjusting the location of the objective lens inside the tube. 

Without the objective lens of the scope, there is no way that light will be able to get to the other lenses of the scope. Therefore, the shooter will not see any image. The objective lens of the scope can simply be termed the initiator of the light collection and transmission system in the scope.

Focus Lens Assembly 

After the objective lens assembly, we have to travel backwards in the scope for us to get to the eyepiece and, finally, the shooter’s eye. 

The next type of lens we will meet on our way to the shooter’s eye is the focus lens. The focus lens of a riflescope is contained in the focus lens assembly. This lens has the option of being adjustable or fixed. 

The focus lens of a scope that is fixed is factory configured to be parallax-free at a certain range, typically 100 yards. For riflescopes that have a parallax adjustment knob, this knob is rotated to compensate for parallax at different ranges. This compensation is done by moving the focus lens assembly further away or closer to the objective lens. 

In reality, this implies that when the knob is adjusted towards infinity, the focus lens is moved closer to the scope’s objective lens. When correcting for nearer objects, the assembly is moved backwards in the direction of the ocular lens. In general, parallax-adjustable scopes may be dialed in to make it parallax-free at distances ranging from 50yards to infinity.

Erector Assembly

The magnifying lenses and reticle components are held in the erector tube assembly. The erector tube is responsible for “erecting” the image, that is, generating an upright image. Let us find out more about this tube assembly.


Moving rearward in the scope tube towards the ocular lens, we reach the erector tube. The erector lens assembly is responsible for housing the reticle assembly and magnifying lenses. When the power ring of a variable scope is turned, the lenses in the erector tube move closer or farther away from the objective lens of the scope. 

What this means is that the erector lens is moved towards the objective lens when you want a higher magnification, and the erector lenses are moved closer to the ocular lens during lower magnification adjustment. 

In other words, when the power ring of a variable scope is turned, the magnifying lenses in the erector tube move to change the magnification. When magnification is increased, the magnification lens advances closer to the objective lens. The lens travels closer to the ocular lens when the magnification is reduced.


The reticle is sometimes known as the “crosshairs.” Reticle can have a cell and this cell can be positioned behind or in front of the magnifying lenses. This makes us have two different focal planes. 

  • First Focal Plane

A first focal plane reticle is one that has the reticle in front of the lens. In this kind of setting,  a change in the scope’s magnification will cause the reticle to change size in relation to the shooter.

In actuality, the reticle remains constant in size in reference to the target. The reticle retains its relative size. If a target is 5 dots tall at lower magnification, it will still be 5 dots tall at higher magnification, implying that all holdover, range, and elevation calculations remain the same at all magnification settings. 

  • Second Focal Plane

A reticle that is on the second focal plane reticle is located behind the magnifying lenses. The reticle retains its absolute size from the shooter’s perspective but shrinks or expands with respect to the target when the magnification is modified. 

The disadvantage is that ballistics or range calculations are only valid at a single power level and must be recalculated with each magnification adjustment.

There are several reticles available. Some are basic crosshairs, while others have three posts. Some reticles contain a calibrated system of dots or hash markings along the hairs to help with calculations of on-the-fly range, holdover, and windage correction. These are known as MIL-DOT reticles. 

We also have illuminated and nonilluminated reticles. The illuminated reticles can further be divided into the red or green illuminations. 

Every shooter may have their preference when it comes to the illumination to choose from. The kind of reticle that is best for you will be determined by how you want to shoot your rifle. It will also be determined a lot by the lighting conditions you anticipate. There are no hard rules when it comes to choosing reticles. Just pick one that works for you.

*Windage and Elevation

The erector tube is also responsible for windage and elevation adjustment. How is this done? 

The erector tube is pressed against the bottom parts of the elevation and windage screws by a spring mechanism to hold the tube in place. When the adjustment screws are pressed or turned inward, the erector tube is pushed against the spring system; when the screws are turned back, the tube is moved away from the spring system. This set-up helps to move the erector tube for elevation and windage compensation.

erector tube
Credit: Hawkeoptics

The erector tube also acts as a connection point between the reticle and the adjusting knobs. The springs and spindles that run back to the knobs make contact here. The erector tube is moved as you make adjustments. 

People are often surprised when they look through a scope while changing the elevation or windage. The reticle appears to be moving in the other way. This occurs because the picture delivered to the erector is upside down. When windage or elevation is dialed in, the erector tube’s front is pushed down (the erector spring is compressed) while the rear pivots upwards, making the reticle look higher in relation to the target. 

To re-acquire your target, the barrel must be angled downward; that’s where the elevation decrease comes from. When the height is increased, the exact reverse happens. Windage operates similarly to elevation but in the horizontal plane rather than vertical. 

To acquire the entire range of adjustments, you must have a fully working erector spring. A cheap or old spring might impede operation.

Ocular Assembly

The ocular assembly is the final destination on our riflescope internal anatomy tour. This assembly comprise the scope’s eyepiece. Also, this is the part where the diopter is changed, allowing users to bring the reticle in focus by altering the location of the ocular lens. It is critical to avoid over-adjusting the ocular lens. 

This adjustment’s sole purpose or aim is to sharpen and focus the reticle; do not attempt to focus the target image with the diopter!

Optical Properties to Note 

I’m going to take a break from anatomy to discuss some optical qualities that are significant in riflescopes. It becomes a little jargon at this point.


The first thing to mention is magnification, or power as some call it. A scope’s magnification is simply how much the image is magnified. The image seen via a 4X power scope seems four times bigger than it would have appeared to the naked eye. This is indicated as a range in a variable scope, such as 4-12X. This means that the scope adjusts the image from 4 times bigger to 12 times bigger. 

Scopes are frequently labelled by objective lens diameter and magnification range; thus, a scope labeled 3-12X50 has a magnification of 3-12 and an objective lens of 50mm. 

Exit Pupil

The exit pupil is the next characteristic to consider. This is a computed parameter, not a measured one. Exit pupil diameter measures the size of the light beam that exits the ocular lens and enters the shooter’s eye. The diameter of the exit pupil is derived by dividing the objective lens in mm by the magnification. As an example, a scope that has a 50mm objective lens and a 5X magnification will have a 10mm exit pupil.

The exit pupil diameter of a riflescope is more important in low-light situations, such as for dusk and dawn shooting. A scope with at least 5mm of exit pupil diameter is a good place to anchor because the pupil of your own eye is in that range, 

Eye relief

Eye Relief

Eye relief is a measured parameter. It is the distance between the eye and the ocular lens required to see the exit pupil of the scope. The most crucial thing to remember while selecting a scope for eye relief is the recoil of the rifle. If you have a high-powered rifle that delivers a great deal of punch after every shot, then you should not go for a scope with a smaller eye relief. 

Make sure your scope has ample eye relief so that you can keep your face safe. It’s also worth noting that as magnification increases, so does eye relief. At greater magnifications, your eye must be closer to the scope to capture the whole view. 

Field of View

Field of view is how wide you can see when you look through the scope. It is commonly described in terms of specific range; for instance, FOV is 40″ at 100 yards signifies that your scope image is 40 ft wide at 100 yards. In a variable scope, this number is expressed as a range, with the field of view shrinking as the magnification increases. When monitoring moving targets, a broad FOV makes the target less likely to go out of your view.


Parallax is observed when the target and the reticle are not on the same plane. Parallax error is a condition in which the reticle shifts its location or aimpoint on the target as the eye moves, which can obviously skew your accuracy. There are scopes that have fixed focal points and are meant to be parallax free at a specific range, which is often 100 yards. 

Other scopes offer parallax compensation adjustments, which may be done using an adjustable objective or a side focus knob. Parallax is decreased or eliminated in either situation by altering the relative locations of the focus lens and objective lens, as explained above. 

At low magnifications, parallax is rarely a concern, but it may become an issue at higher magnifications.

Other scope terminologies

Coatings for Lenses

To accomplish precise outcomes, riflescope manufacturers use a variety of unique coatings for the surfaces of their lenses. Some lens coatings are intended to improve picture clarity. Lens coatings also minimize glare and thereby increase light transmission.

Another use of lens coating is to improve scratch resistance so that the lens is not damaged by rigorous handling.


Purging, which was formerly considered unique, is now considered industry standard. To prevent condensation and moisture from entering the scope, the manufacturer fills it with an inert gas like nitrogen or argon. This procedure keeps scope lenses from fogging, extending the scope’s effectiveness regardless of weather or ambient temperature.


When choosing a sight for your rifle, be sure it’s rated for the amount of recoil your gun produces. A riflescope created for a 22-caliber rimfire round cannot withstand a centerfire round.

Scope Ring 

A scope ring is not actually a rifle scope component but an essential part of riflescope mounting. Scope rings wrap the main tube at two points, fore and aft, and are used to mount the scope to the base mount or rifle.


When you want to mount a sight, make sure the optic clears the bolt handle and the hammer. The bolt throw – the rotation of the bolt from open to closed — will also have an impact on the required scope clearance.

Scope Bite

The distance between the eyepiece and shooter’s eye is referred to as eye relief. A long eye relief is necessary for effective shooting, but it is also necessary for your safety. If you get too close to the eyepiece of your scope, the recoil may injure your eye. This injury is what is known as a scope bite.

What Is The Best Way To Clean The Internal Anatomy Of A Riflescope?

The answer is very simple: don’t do it. The interior parts of a rifle scope cannot be cleaned at all by the user. You can only clean the external surface of a lens when it becomes filthy using things like smooth cloth, lens brash, and so on.

If your scope has an internal fault or anything else is wrong with it, you should return it to the manufacturer. Because modern rifle scopes are usually sealed with inert gas, it’s a bad idea to try to open the internal parts.

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