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Rifle Scope Glossary of Terms

Aug 17, 2023 | 05:39 pm 223 0
Rifle Scope Glossary of Terms

When you decide to buy new equipment, you need to understand what parameters you will pay attention to when choosing a specific model. And it is always tricky, especially in cases where you are faced with a list of questions to answer for the first time.  Understanding and being able to explain these questions is essential because, in the future, it will help you navigate the market and choose what meets your needs.

And this applies to different areas of life. When you choose a scope for your rifle, this is no exception. Let's say you decide to buy a gun for hunting for the first time. You open a website with goods, and your eyes run away from the number of items in the store. Many options are scrolling on the site, you look at the prices without understanding why they are so high, and when you read the technical characteristics of the optics, you see a bunch of terminology that tells you nothing.

So before you buy a specific model of a scope, you should understand the terms and characteristics of the device to choose what you need and spend money wisely on something that will make the hunting process more accessible, not vice versa. After all, this is entirely possible in the case of an incorrectly selected device. 

That's why today we will look at a list of terms and their interpretations that are important to understand before buying a scope.

Let's start with the simple and basic: what is an optical sight?

A riflescope is an optical device designed to aim a weapon at a target accurately. It can also be used to observe the terrain and determine distances to objects. Such a sight simplifies the aiming process and increases accuracy, which is essential for long-range shooting. The tubular metal body contains three lens systems: a lens, an eyepiece, and a rotating system. A reticle (mark) is located in the focal plane. 

The lens is responsible for the image quality. It collects the light flux and builds a picture on the focal plane. The eyepiece helps to see the image formed by the lens.

The eyepiece is a multi-lens design designed to view a magnified direct image of the target and reticle. A rubber eyepiece is often worn over the eyepiece to avoid glare and illumination of the eyepiece lens and to ensure accurate eye fixation in the entire field of view of the reticle.

The Rotary system converts the inverted image created by the lens into a straight image.

Focal plane - the surface on which the image formed by an optical device is formed.

Light-gathering power refers to the ability of a lens to collect light. Aperture can be calculated as the square of the lens diameter in millimeters. 

Resolution is an essential indicator of how well an optical sight can distinguish fine details and provide a sharp image. The higher the resolution, the more intense the colors appear. The resolution depends on the size of the lens. 

Eye Relief is measured in inches and indicates how far the eye must be from the reticle for the shooter to see the entire field. 

The field of view is the width of space seen through the eyepiece. The linear field of view is measured in feet per 100 yards. As the magnification of a scope increases, its field of view decreases. For example, a conventional variable magnification riflescope may have a field of view of 30 feet per 100 yards at a magnification 3x but only 14 feet at a magnification of 9x. Changing the size of the objective lens does not affect the size of the field of view.

When choosing an optical device, you can repeatedly find information about the lens coating in the specifications. It is used to brighten the image. The classification of this coating depends on its type, number of layers, and their quality.  The following terms can be found in the descriptions of riflescope specifications.

Coated means that the lens is covered with a single layer of anti-reflective coating, mostly on one side of the lens. 

Fully Coated - a single layer of clarifying coating is applied to all glass surfaces in contact with air.

Multicoated - the lens is coated on one side but with several coating layers. 

Fully Multicoated is when several layers of coating are applied to all lens sides. As a rule, the higher the quality of this coating, the more precise and more contrasty the image will be. 

The reticle applied to one of the lenses will play a significant role in the accuracy of your shot with the riflescope. This is a scale that facilitates the aiming process. There are many variants of reticles: many manufacturers create schemes of this scale, which are adapted for shooting different cartridges at different distances, etc.

The main types of reticles.

Mil-Dot is one of the most famous sighting systems for airguns. It consists of two coordinate axes with equidistant markings. The marking division is 1 minute of angle (MOA). It is easy to use and allows you to determine the distance to the object of observation with knowledge and skill. 

The 30/30 grid is the intersection of two lines of equal thickness. It is in demand among firearms enthusiasts. Duplex is one of the variations of this mesh that has a thickening in the peripheral areas of the axes.

Ballistic. This type of reticle has several aiming points calibrated to typical distances, making it much easier to shoot with range adjustments. There are also varieties of ballistic reticles with additional side marks to account for the wind displacement of the bullet. 

It is important to remember that no matter how accurate and perfect your reticle is, once you have installed the optical device on your weapon, you must practice and adjust the position of the reticle. This is necessary to ensure that the aiming point coincides with the center point of impact. To do this, the scope design includes a correction mechanism - special handwheels that move the reticle vertically and horizontally by a specified MOA. 

Minute of Angle is a unit of measurement within a circle. MOA is the leading standard for determining the accuracy of a rifle. This angular width is almost exactly one inch at 100 yards, then expands to two inches at 200 yards, three inches at 300 yards, and so on, up to 10 inches at 1000 yards, and so on.

Each sight is equipped with a mechanism for making corrections in two mutually perpendicular directions: vertically ("range") and horizontally ("offset"). Multi-position correction controls are completed as drums, also called turrets. 

The turrets are divided into two types: tactical and traditional hunting turrets. Tactical turrets are designed for correcting the CCT in combat conditions: without additional tools, without looking, counting clicks by ear. They are also better protected than conventional ones from accidental resetting and moisture and dust particles getting into mechanical components. Unlike tactical turrets, hunting turrets may require more complex manipulations to enter the settings, which must be performed before you go hunting.

When you are adjusting the shooting process with a scope, you should keep in mind the phenomenon of parallax. Most people understand what parallax is with experience when they have directly encountered it during work. Most scopes with a medium magnification range of 10x or a little more, which often do not have an internal parallax correction mechanism, are factory corrected for 100 or 150 yards (91, 4, and 137 m). If you have already purchased an optical device, you can check this as follows. Take one scope that is adjusted for 100 yards, set its magnification to maximum by aiming the crosshairs at the center of the target at a distance of, say, 25 yards, and then move your head slightly to the left or right, up or down. You'll see that the crosshairs have also moved away from the center, even though the reticle itself doesn't move. The same happens when their target is set to a longer distance, say 300 yards.

The internal parallax correction mechanism on the lens is usually installed on scopes with a magnification higher than 10x or on scopes used at close ranges. The parallax correction ring is located on the lens barrel. It has divisions with marks corresponding to certain shooting distances. Recently, scopes with a parallax correction drum on the left side of the central part of the reticle's axial tube in the standard adjustment unit of the reticle mechanisms have become popular. For the shooter, this layout seems more convenient.

Remember, parallax correction is usually not required for hunting scopes with a 10x or lower magnification (perhaps even slightly higher). Often, parallax correction is optional for accurate hunting. For most game species, the size of the kill zone is quite large, so the effect of parallax on hit accuracy is negligible.

Airgun scopes and high-powered scopes always have a parallax correction mechanism. Rifle scopes with ring-ignition cartridges are often adjusted at 60 yards, shotgun scopes at 75 yards, and the rest at 100 and 150 yards.

An integral characteristic of a scope is its magnification. This is the degree of elaboration of the observed object about you. The degree of exaggeration should be chosen depending on the distance from which you plan to shoot. Sights with a magnification of 3x-9x or 3x-12x are considered universal: they are best suited for hunting. It is better to pay attention to models with magnifications of 6x-24x and 8x-32x for long-range shooting or targeting paper targets. 

The magnification of the scope and the diameter of its objective lens determine the exit pupil diameter (EPD), the most important parameter characterizing the size of the light beam coming out of the eyepiece. Calculating this value is very simple: divide the objective diameter by the magnification, i.e., for an 8x32 scope, we get 32/8 = 4 mm. The larger the IE, the brighter and lighter the image, which is essential for shooting at dusk or if the shooter has imperfect eyesight. An exit pupil of more than 7-8 mm will completely block the human pupil, so there is no particular reason to design such sights. An exit pupil with a diameter of about 5 mm is optimal.

The exit pupil distance characterizes the optimal position of the shooter's eye relative to the eyepiece lens. Structurally, it is possible to ensure that this value is independent of the magnification of the reticle. Still, the pupil distance correlates with the focal length of the eyepiece. For shooting optics, the exit pupil distance can range from 40 to 105 mm, depending on the weapon's purpose. For light pneumatics, a distance of 4-4.5 cm is recommended; for large-caliber firearms - at least 7.5 cm; for shotguns - at least 8 cm. The increased pupil distance reduces comfort during aiming but ensures eye safety when shooting pellets and during the recoil of a shot.

The scope body is made of durable, lightweight alloys. It combines all sight components into a single structure that must ensure high resistance of the sight systems and mechanisms to shock loads arising during shooting, as well as the weight of the device itself. This is also an important parameter. 

The weapon must have a suitable mounting base to mount the sight: Weaver/Picatinny or dovetail mounts. The riflescope is mounted to the rail with unique rings that differ in diameter and height depending on the size of the riflescope. The most common mounting rings are Ø 25.4 and 30 mm. The height of the mount will depend on the diameter of the riflescope objective lens: only high mounts are suitable for large lenses, and any horses are ideal for small ones. The mount rings can be made in the form of a monoblock or can be supplied separately. The first mounting option provides a more rigid fixation and is recommended for mounting on weapons with high recoil.

At first glance, such an extensive list of terminology and parameters to consider when choosing an optical device may need to be clarified. After all, more is needed to understand the autonomous function of each of them. It is essential to understand their combination for productive work. But not everything is as scary as it might seem at first glance. After all, manufacturers have already handled this and provided examples of the best options to meet your needs. Now you know what these indicators mean and what to expect from the scope. 

The first thing you will still need to consider is your requirements for this optic. For example, riflescopes with a magnification of up to 4x are appropriate for shooting at moving targets. If its multiplicity exceeds this mark, such options are more suitable in situations where you have support, and your target is stationary.

Buying such a thing is risky when you have never held or used it. Therefore, after a short tour of the online store, it is better to visit a physical store and consult with someone who already has experience in these matters. It is excellent if you have the opportunity to visually check and understand each of the above terms in practice and how they affect the functionality of the optical device. In this case, you can consult a specific scope on how to deal with such a phenomenon as parallax, which we mentioned earlier. 

The main thing to remember. That everything comes with experience. It is impossible to memorize and understand everything at once. But you have already made the first step towards understanding an optical sight.

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