The invention of the rifle scope as an adaptation of the telescope literally revolutionized the art of long range, precision, shooting. While there are some unconfirmed stories of a couple of the 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’s 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. Consequently, today telescopic rifle scopes are so deeply imbedded in our collective hunting and shooting psyche that the idea of having an open-sighted, long range, rifle literally seems foreign to us! But, if you are going to purchase a rifle scope to mount on your favorite rifle, then you should know what features are important and how to compare one feature to another.
For instance, to start with you need to understand that a rifle scope consists of either a single-piece or a multi-piece metal tube which contains a series of external and internal glass lenses along with an adjustable aiming device called a Reticle. Also, you need to understand that all rifle scope lenses are made from optical quality glass because high quality glass provides the clearest possible image. Then, you need to understand how to identify each part of the rifle scope and what purpose it serves. Next, you need to understand how each feature of the rifle scope affects its performance in order 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 rifle scope over another in order to determine which scope is best suited for your particular purpose.
Therefore, let’s start with how to identify each part of a rifle 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 which contains the Objective Lens.
- Objective Lens – The Objective Lens is the glass lens placed farthest from the shooter’s eye and which gathers the ambient light that is 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: Has a single layer of coating on at least one lens surface.
- Fully Coated: Has a single layer on all air to glass surfaces.
- Multicoated: Has more than one layer of coating on at least one lens surface.
- Fully Multicoated: Has multiple layers of coating on all air to glass surfaces.
- Field of View – The Field of View is the horizontal range of view a rifle scope encompasses measured in yards and is dependent on the diameter of the Objective Lens. 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 which enable the shooter to adjust the relative position of the reticles in order 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 which 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 that is 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 and, the larger the exit pupil is, the brighter the sight picture is.
- Reticle – The Reticle is the arraignment of crosshairs, posts, ect. that is superimposed over the sight picture when the shooter looks through the Ocular Lens.
- Power Ring – The Power Ring is the ring located just forward of the Eyepiece and, 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 which focuses the image correctly on the Reticle Plane (not the Ocular Plane) at varying distances.
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 important 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 because it makes it easier to spot your target and track it if it moves. However, 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 and the larger the diameter of the Objective Lens is, the more ambient light it is able to collect and transmit through the scope tube to the Ocular Lens. Thus, larger the diameter of the Objective lens, the larger the Exit Pupil is and thus, the brighter the sight picture is at any given ambient light level. However, rifle scopes with larger Objective Lenses do 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 and thus, it does not enter the scope. This, in turn, reduces the brightness of the sight picture. However, any light that strikes a glass lens at an angle greater than 45° passes through the lens and enters the scope tube, thus providing the shooter with a sight picture. Consequently, coating rifle scope lenses reduces the amount of light lost to reflection and different types of lens coatings affect the amount of reflection as well as the clarity of lens’s focus and the amount of light transmitted through the scope tube to the Ocular Lens. Therefore, two popular lens coatings are Magnesium Fluoride and the mineral Corundum (aka Ruby).
- Exit Pupil – The reason that the size of the Exit Pupil is important to the shooter is that the larger the Exit Pupil is, the more light that is transmitted through the scope tube to the Ocular Lens and, the more light that arrives at the Ocular Lens, the brighter the sight picture is in 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 the 95% is the theoretical limit of the maximum amount of light a rifle scope can transmit, some scope manufactures claim to have exceeded that theoretical limit in some models.
- Eye Relief – The amount of Eye Relief a rifle scope has is important to the shooter because some shooters like to place their eye as close to the Ocular Lens as possible in order to block out ambient light while others prefer to have it placed farther away from their eye due to the fact that heavy-recoiling rifles can cause the Eyepiece to impact the shooter’s eye socket (ouch!!!). Therefore, it is important to choose a rifle scope with an Eye Relief that is appropriate for both the shooter and the caliber of the rifle.
- Reticles – Reticles are available in several different types and each type has as specific purpose. However, the most popular type of reticle is the “Crosshair” which is available in Fine, Medium, and Heavy and, while Fine Crosshairs are normally used for long range shots or for hunting small game, Medium Crosshairs are normally used for large game at medium ranges, and a Large Crosshairs are normally used for hunting large, dangerous, game at close ranges and/or in heavy foliage where acquiring the target quickly is of paramount importance. Another popular type of reticule 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 type of reticle that is popular with 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 has 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 reticule 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 with consist of a Duplex Reticle with three cross hairs of differing lengths placed on the bottom half of the vertical crosshair below the main crosshair.
- Magnification Range – Rifle scopes are available with either a fixed-power magnification or a variable-power magnification. Also, variable power rifle scopes are available with a wide range of magnification settings such as 3-9, 4-12, 4.5-30, ect. However, each type has its own advantages and disadvantages. For instance, fixed-power scopes require fewer internal lenses and thus, they are both lighter and more rugged than variable-power scopes because they have fewer moving parts. However, variable-power rifle scopes enable the shooter to quickly change the magnification of their scope for either short, medium, or long range shots. For instance, 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. Thus, 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 serve the purpose of enabling the shooter to move both the vertical and horizontal reticles up or down and right or left separately in order to adjust the bullet’s point of impact on the target. In addition, rifle scopes have one of two different types of turrets depending on their purpose. For instance, hunting scopes generally have low profile turrets that are designed to be adjusted with a coin whereas tactical/target rifle scopes generally have high profile turrets that are easily adjusted with the shooter’s fingers. In addition, as a general rule, each “click” on either type of turret equals ¼” of adjustment left/right or up/down at 100 yards. Therefore, 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 Fogpoofing – Due to the fact that early rifle scope tubes were not purged of air and then sealed (called negative pressure), they were subject to the vagrancies of the ambient air pressure and humidity. Thus, the lenses were prone to fog up whenever the air became moist and could even collect water inside of the scope tube if the rifle were accidently dropped while crossing 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 thus, fog up the lenses.
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? Well, that depends on what type of hunting or shooting you intend to pursue. For instance, 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. However, if you are hunting over large agricultural fields of the Mid-West or on the open ranges of the West, then you would definitely want a scope with a variable power range and either fine or medium crosshairs because the large majority of your shots are likely to be taken at ranges of 100 yards or more.
Also, when hunting in low ambient light conditions, you would want a scope with a large Objective Lens so that it can collect the maximum amount of light possible for the clearest possible sight picture. In addition, remember that when you increase the magnification of a rifle scope, you also decrease the size of the Exit Pupil and thus, a rifle scope with a larger Objective Lens will provide a brighter sight picture at higher magnifications because it has a larger Exit Pupil. In addition, the type and number of coatings on the lenses are of significant importance because they will affect both the amount of light transmitted through the scope tube and the clarity of the sight picture. Thus, the more lenses that are coated and the more coatings each lens has, the better (but more expensive too). Plus, you also need to choose 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 style of shooting.
Furthermore, if you are planning on consistently shooting at very long ranges, then you should consider a scope with high profile target/tactical turrets to enable you to quickly and easily make adjustments to your bullet’s point of impact due to changes in wind speed, elevation, or humidity. Also, you should look for a model with a Parallax Adjustment Ring so that you can quickly and easily adjust the amount of Parallax in your scope for a clear sight picture at varying ranges. Last, you definitely want to purchase a scope that is designated as waterproof and fogproof and scopes filled with Argon/Krypton gas mixture are better than scopes filled with Nitrogen gas because the Argon and Krypton atoms are significantly larger than the Nitrogen atom and thus, the Krypton and Argon atoms are less likely to migrate from the hypertonic atmosphere inside of the scope tube to the hypotonic atmosphere outside of the scope tube.