Are you looking for an accurate rifle scope to help you hit your targets? If so, you may be wondering about the specs that come with a scope. Here is a brief guide on the parts of a scope, their effects, and what you should look for when purchasing a scope.
The invention of the rifle scope as an adaptation of the telescope revolutionized the art of long-range, precision shooting. While there are some unconfirmed stories of a couple of famous, old Buffalo hunters such as “Wild Bill” Cody, who were sometimes able to hit a Buffalo at 1,000 yards with their Sharps 45/70 and 45/100’s and their Vernier peep sights, this type of precision shooting was far beyond the ability of the average shooter.
However, the concept of attaching a specialized telescope to the top of a rifle suddenly made the art of long-range, precision shooting available to a much wider range of shooters. Today telescopic rifle scopes are so deeply embedded in our collective hunting and shooting psyche that the idea of having an open-sighted, long-range rifle seems foreign to us! If you purchase a rifle scope to mount on your favorite rifle, you should know what critical features to look for. You should also know how to compare features.
Tto start with, you first have to know that a rifle scope consists of either a single-piece or a multi-piece metal tube that contains a series of external and internal glass lenses along with an adjustable aiming device called a Reticle. You need to understand that all rifle scope lenses are made from optical-quality glass because high-quality glass provides the clearest possible image.
You must figure out how to identify each part of a rifle scope and its purpose. You need to understand how each feature of a rifle scope affects its performance to have enough knowledge to compare one rifle scope to another and, thus, be able to evaluate the merits of one brand or model of a rifle scope over another to determine which scope is best suited for your particular purpose.
Parts of a Scope
- Scope Tube – The Scope Tube is the metal tube that contains all of the internal and external parts that comprise a rifle scope.
- Windage Bell – The Windage Bell on a rifle scope is the end of the scope farthest from the shooter’s eye and contains the Objective Lens.
- Objective Lens – The Objective Lens is placed farthest from the shooter’s eye. It gathers ambient light transmitted through the scope tube to the Ocular Lens.
- Lens Coatings – Lens coating refers to the microscopic layer of chemical coating that is applied to the external glass surfaces of the rifle scope, and there are four different euphemisms used to describe lens coatings:
- Coated: At least one lens surface is coated.
- Fully Coated: Contains a single layer of coating on all air-to-glass surfaces.
- Multicoated: At least one lens surface is coated with more than one layer.
- Fully Multicoated: Coated on all air-to-glass surfaces multiple times.
- Field of View – The Field of View is the horizontal range of view a rifle scope encompasses, measured in yards and dependent on the objective lens’s diameter. It is defined as the width in feet or meters of the area visible at 100 yards or meters through the scope.
- Turrets – The turrets on a rifle scope are the round protrusions on the top and side of the scope tube. These protrusions enable the shooter to adjust the relative position of the reticles to change the bullet’s point of impact.
- Eyepiece – The Eye Piece on a rifle scope is the bell closest to the shooter’s eye and contains the Ocular Lens. By rotating the Eye Piece left or right, the shooter can adjust the focus of the sight picture.
- Ocular Lens – The Ocular Lens is the glass lens closest to the shooter’s eye.
- Exit Pupil – The exit pupil is the size of the column of light that leaves the eyepiece of a scope. There is a direct correlation between the size of the exit pupil and the brightness of the sight picture.
- Reticle – The Reticle is the arrangement of crosshairs, posts, etc., superimposed over the sight picture when the shooter looks through the Ocular Lens.
- Power Ring – The Power Ring is located just forward of the eyepiece. By rotating the Power Ring left or right, you can increase or decrease the magnification of the sight picture on variable power scopes.
- Parallax Adjustment Ring – A ring on the Windage Bell that bears hash marks designated for different yardages and correctly focuses the image on the Reticle Plane (not the Ocular Plane) at varying distances.
Rifle Scope Specifications: How They Affect Accuracy and Shooting Experience
Now that you know how to identify each part of a rifle scope and what function it performs, you need to learn what features of a rifle scope are most significant to you as a shooter and how they affect the performance of the rifle scope and thus, your ability to hit your chosen target at extended ranges:
- Field of View – A wide field of view is desirable in a rifle scope. This is because it makes it easier to spot your target and track it if it moves. As a general rule of thumb, the higher the magnification setting, the narrower the field of view is.
- Objective Lens – The diameter of the Objective Lens on all rifle scopes is measured in millimeters. The larger the diameter of the Objective Lens is, the more ambient light it can collect and transmit through the scope tube to the Ocular Lens. The larger the diameter of the objective lens, the larger the exit pupil. Thus, the brighter the sight picture is at any ambient light level. However, rifle scopes with bigger Objective Lenses require taller scope mounts to allow for the increased diameter of the Windage Bell.
- Lens coatings – Any time light strikes a glass lens at an angle of less than 45°, that light is reflected away; it does not enter the scope. This reduces the brightness of the sight picture. Any light that strikes a glass lens at an angle of more than 45° passes through the lens and enters the scope, providing the shooter with a sight picture.
- Coating rifle scope lenses reduces the amount of light lost to reflection. Different types of lens coatings affect the amount of reflection, the clarity of the lens’s focus, and the amount of light transmitted through the scope tube to the Ocular Lens. Two popular lens coatings are Magnesium Fluoride and the mineral Corundum (aka Ruby).
- Exit Pupil – The size of the Exit Pupil is crucial to the shooter because the larger the Exit Pupil is, the more light is transmitted through the scope tube to the Ocular Lens. The more light arrives at the Ocular Lens; the brighter the sight picture is at any given ambient light level. To determine the size of the Exit Pupil, divide the diameter of the Objective Lens by the level of magnification (ex., a 4 x 32mm scope has an exit pupil of 8mm).
- Light Transmission – A rifle scope that transmits a higher percentage of light presents a brighter sight picture to the shooter. However, although 95% is the theoretical limit of the maximum light a rifle scope can transmit, some manufacturers claim to have exceeded that limit in some models.
- Eye Relief – The amount of eye relief a rifle scope has is critical for the shooter because some shooters like to place their eyes as close to the Ocular Lens as possible to block out ambient light. Others prefer to have it placed farther away from their eyes since heavy-recoiling rifles can cause the eyepiece to impact the shooter’s eye socket (ouch!!!). Therefore, it is imperative to choose a rifle scope with eye relief that is appropriate for both the shooter and the caliber of the rifle.
- Reticles – Reticles are available in several different types, each with a specific purpose.
- The most popular type of reticle is the “Crosshair,” which is available in Fine, Medium, and Heavy.
- Fine crosshairs are typically used for long-range shots or hunting small game.
- Medium crosshairs are normally used for large game at medium ranges.
- Large/heavy crosshairs are normally used for hunting large, dangerous game at close ranges and/or in heavy foliage where rapidly acquiring the target is paramount.
- Another popular type of reticle for close-range hunting is the Duplex Reticle which consists of bars that are quite wide near the perimeter of the scope and yet, are quite narrow in the center of the lens, which enables the shooter’s eye to pick up the reticle quickly against a complex background or in a tense shooting situation and then use the fine crosshairs to achieve a fine point of aim.
- A third type of reticle that is popular for hunting at close ranges is the Target Dot reticle which consists of a set of medium crosshairs and a medium-sized dot in the center of the crosshairs, which, once again, allows the shooter to pick up the point of aim very quickly in a tense shooting situation.
- Last, another reticle that is a favorite of long-range hunters is the Mil-Dot reticle which enables the shooter to employ the “Kentucky Windage” technique by placing the horizontal and vertical crosshairs (which have several small dots superimposed on them) on the target and then moving the horizontal reticle right or left the correct number of dots and then moving the vertical reticle up or down the correct number of dots according to a trigonometric formula to achieve the correct point of aim.
- However, there are also other, less popular, types of reticles available such as the German reticle, which consists of a wide, pointed post extending vertically from the bottom edge of the lens to the center of the lens with two short, wide, bars extending horizontally one half of the distance from the sides of the lens to the point on the post. Another less popular type of rifle scope reticle is the Rangefinding Reticle, consisting of a Duplex Reticle with three crosshairs of differing lengths placed on the bottom half of the vertical crosshair below the main crosshair.
- The most popular type of reticle is the “Crosshair,” which is available in Fine, Medium, and Heavy.
- Magnification Range – Rifle scopes are available with either fixed or variable-power magnification. Also, variable power rifle scopes have many magnification settings, such as 3-9, 4-12, 4.5-30, etc. Each type has its advantages and disadvantages. Fixed-power scopes require fewer internal lenses. They are lighter and more rugged than variable-power scopes because they have fewer moving parts.
- Variable-power rifle scopes enable the shooter to quickly change the magnification of their scope for either short, medium, or long-range shots. For hunting large game in heavy cover, you might choose a fixed 1.5X scope or a variable 3-9X scope set to 3X so that you can acquire the target quickly. But, for hunting at long ranges, you would be better off with a fixed, 4X scope, a variable 3-9X, or a variable 4-12X scope.
- Parallax – This is a condition that occurs when the image of the target is not focused precisely on the Reticle Plane (located at the turrets near the center of the scope tube) and is visible as an apparent movement between the reticle and the target when the shooter moves their head or, in extreme cases, as an out-of-focus image.
- By rotating the Parallax Adjustment Ring on the Windage Bell to the hash mark that matches the range at which you are shooting, the Objective Lens is properly focused on the Reticle Plane for a clear sight picture.
- Turrets – The turrets on a rifle scope enable the shooter to move both the vertical and horizontal reticles up or down, right or left, separately. Allowing the shooter to adjust the point of impact on the target. Rifle scopes have one of two different types of turrets, depending on their purpose. Hunting scopes generally have low-profile turrets designed to be adjusted with a coin.
- In contrast, tactical/target rifle scopes generally have high-profile turrets that are easily adjusted with the shooter’s fingers. As a general rule, each “click” on either type of turret equals ¼” of adjustment left/right or up/down at 100 yards. This type of adjustment is called a 1/4 Minute of Angle adjustment because one M.O.A. equals one inch at 100 yards.
- Waterproofing and Fogproofing – Early rifle scope tubes were not purged of air and then sealed (called negative pressure), they were subject to the vagrancy of ambient air pressure and humidity. The lenses were prone to fog up whenever the air became moist. They could even collect water inside the scope tube if the rifle were accidentally dropped while crossing a stream or wading in a swamp.
- Therefore, rifle scope manufacturers have invented a process that enables them to evacuate all of the air from a scope tube and replace it with either Nitrogen or an Argon/Krypton gas mixture (both of which are inert) and then seal the scope tube with rubber O-rings to maintain the positive internal pressure so that moist air cannot enter the scope tube and fog up the lenses.
How to Choose the right Rifle Scope for You
So, now that you understand what all the different parts of a rifle scope are and what function they perform, as well as the many different features available on modern rifle scopes, what features do you look for when purchasing a rifle scope?
That depends on what type of hunting or shooting you intend to pursue. If you are hunting at close range, in heavy cover, with low ambient light, you might want a fixed power scope with a magnification of 1.5X to 3X (provides a larger exit pupil) with either a Duplex or a Target Dot Reticle.
If you are hunting over the large agricultural fields of the Mid-West or on the open ranges of the West, then you would want a scope with a variable power range and either fine or medium crosshairs because the vast majority of your shots are likely to be taken at ranges of 100 yards or more.
When hunting in low ambient light conditions, you would want a scope with a large objective lens to collect the maximum amount of light possible for the clearest image. Remember that when you increase the magnification of a rifle scope, you also decrease the exit pupil size. A rifle scope with a larger objective lens will provide a brighter sight picture at higher magnifications because it has a larger exit pupil.
The type and number of coatings on the lenses are important because they affect both the amount of light transmitted through the scope tube and the clarity of the sight picture. The more coated lenses and coatings each has, the better (but more expensive).
Chose a scope with the correct amount of Eye Relief for the caliber (amount of recoil) of the rifle you are shooting and for your particular shooting style.
Furthermore, suppose you plan to shoot a lot at very long ranges. In that case, you should consider a scope with high-profile target/tactical turrets to quickly and easily adjust your bullet’s point of impact due to wind speed, elevation, or humidity changes. Look for a model with a Parallax Adjustment Ring. This will enable you to quickly and easily adjust the amount of parallax in your scope for a clear sight picture at varying ranges.
Last, you want to purchase a waterproof and fog-proof scope. Scopes filled with an Argon/Krypton gas mixture are better than those filled with Nitrogen gas because the Argon and Krypton atoms are significantly larger than the Nitrogen atom. The Krypton and Argon atoms are less likely to migrate from the hypertonic atmosphere inside the scope tube to the hypotonic atmosphere outside the scope tube.