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Rifle scopes offer the shooter a precision sighting system for accurate and long-range shooting. However, rifle scopes aren’t quite as simple as iron sights.
You must understand some basic rifle scope anatomy to get the accuracy you want from your rifle scope.
Why a Rifle Scope?
Sighting systems are essential for aligning your rifle with your target to achieve an accurate shot. The rifle scope is one of the most effective sighting systems available, allowing you to magnify the target image, increasing the range at which you can clearly see and identify your target.
However, rifle scopes are complex systems. If you’re unfamiliar with how they function, learning the parts of a rifle scope can help you during your selection process.
Basics of Rifle Scopes
A rifle scope is a telescopic sight consisting of a metal tube and a series of lenses that collect and amplify light, transmitting it to your eye in the form of an image. The outside of the scope contains controls in the form of rotary turrets that you use to adjust the magnification (in variable-power designs), windage, elevation, and parallax. In illuminated-reticle designs, there’s also a turret for adjusting the brightness setting.
It’s worth taking a moment to explain how rifle scope designations are written. Take the following example: 1–4×42mm. The first set of numbers denotes a minimum–maximum magnification range in a variable-power scope of 1× to 4×. The second number — 42mm — represents the diameter of the objective lens in millimeters.
The body or main tube houses the lenses supports the external controls and provides an anchor point for attaching the optic to your rifle. This part is usually made from aluminum, which is durable, relatively lightweight, and resistant to corrosion. The strongest designs are manufactured from one piece.
Objective Lens Assembly
The purpose of the objective lens is to collect light and transmit an image of the object you’re observing to the ocular lens. The larger the objective lens, the more light it can collect and the brighter and sharper the image it can deliver. In the scope tube, the housing will flare in some designs toward the front. The wider diameter that contains the objective lens is called the objective bell. The diameter of the objective lens is measured in millimeters.
Erector Lens Assembly
The objective lens transmits the target image upside down to the erector lenses, which correct the orientation of the image and transmit it to the ocular lens. The erector assembly also contains the reticle and moves horizontally and vertically inside the main tube.
When you increase the magnification in a variable-power rifle scope, you’re moving the magnification lenses closer to the objective lens. When you decrease the magnification, you’re moving the magnification lenses closer to the ocular lens. Depending on whether the reticle is affixed to the front or rear of the magnification lens, your reticle image will either be on the first or second focal planes.
1. First Focal Plane
In the first focal plane, the reticle is affixed to the front magnification lens. The size of the reticle changes with the magnification of the target; therefore, increasing the magnification increases the reticle’s size and vice versa.
2. Second Focal Plane
In the second focal plane, which results from the reticle being affixed to the rear magnification lens, the reticle’s size remains fixed at all times. Regardless of whether you increase or decrease the magnification, the reticle remains unchanged.
Ocular Lens Assembly
The light that the objective lens collects and transmits to the erector lenses is then sent to the ocular lens. The ocular lens is contained in the eyepiece and is the part of the scope closest to your dominant eye. You view the target image through the exit pupil — the center of the ocular lens.
Magnification describes the ability of the rifle scope to enlarge the target image. In variable-power rifle scopes, you can adjust the magnification using the power selector ring. There’s a device called a throw lever in some designs, which attaches to the power ring. This allows you to adjust the magnification rapidly to adapt to targets at different ranges.
The reticle, also called crosshairs, is your visual aiming marker. There are a multitude of reticle options, from duplex and mil-dot to BDC (bullet drop compensator).
This turret allows you to adjust the deviation of the rifle scope’s optical axis along the horizontal plane by moving the erector tube assembly to the right or left.
The elevation turret allows you to adjust the deviation of the rifle scope’s optical axis along the vertical plane by moving the erector assembly up or down.
Rifle scope manufacturers apply several special coatings to lens surfaces to achieve specific results. Some lens coatings are designed to enhance image clarity. These coatings reduce glare, thereby maximizing light transmission.
Other lens coatings are designed to increase abrasion or scratch resistance, ensuring that the lens remains unaffected by rough handling.
Once a novelty, purging is now the industry standard. The scope manufacturer will fill the scope tube with an inert gas, such as argon or nitrogen, to protect against the ingress of moisture and condensation. This practice prevents the fogging of scope lenses, preserving the scope’s usefulness regardless of the weather and ambient temperature.
When selecting a scope for your rifle, it’s imperative that you choose one that’s rated for the recoil your rifle produces. A scope designed for .22-caliber rimfire cartridges may not be able to withstand the recoil of a centerfire magnum cartridge.
Scope rings are not strictly parts of a rifle scope, but they’re critical to using one effectively. Scope rings encircle the main tube at two locations, fore and aft, and attach the scope directly to the rifle or a base mount.
The scope ring size that you will need corresponds to the size of the scope. For example, if you have a scope with a 30mm tube, you’ll need a set of 30mm scope rings. The scope rings should be as low as possible to allow for a consistent stock weld, which is important for consistent eye relief.
When mounting a rifle scope, you should take care that the optic will clear the bolt handle and the hammer (in exposed-hammer rifles). The bolt throw — i.e., the rotation of the bolt from open to closed — will also affect the necessary scope clearance.
Eye relief is the distance between the eyepiece and your dominant eye. While consistent eye relief is essential for accurate shooting, it’s also important for your safety. Too close, and the recoil may cause injury to your eye. This is called scope bite.
When choosing a rifle scope, it’s worth taking a look at accessories to protect your equipment and reduce glare. Some examples include scope caps, which protect the objective and ocular lenses from impact or abrasion. Another is a honeycomb cover for the objective lens. This device is designed to reduce glare and reflection that can disclose your position.
Rifle scopes are amazing tools for accurate shooting, whether you’re a hunter, precision shooter, or law-enforcement/military sniper. Learning the basics of rifle scopes can help you choose the optic best suited to your needs.