Only a few decades ago, riflescopes were considered a rare piece of hunting equipment, as, after the end of World War II, the prices of these optical devices were almost unimaginably high. With the progress of serial production and the rise of more manufacturers, the prices of riflescopes have dropped significantly. Today, it is only on a rare occasion to come across a modern centerfire hunting rifle that is not equipped with a riflescope. Namely, the riflescope significantly improves the accuracy and the efficiency of the shooter’s range when compared to the rifles equipped with only traditional iron mechanical sights. In fact, the riflescope even raises the level of hunting ethics, as its use has significantly reduced the number of trailing wounded game and remains a must-have in every hunter’s equipment.
Magnification and Lens Diameter
As with all optical devices, magnification is one of the most important features of a riflescope. The first number in the product’s name is usually the magnification power, which is located right after the name of the producer. The second number depicts the size of the lens diameter. Riflescopes can have fixed magnification and are, in this case, marked with only two numbers. Like, for example, 6×42, which suggests that such a scope has a 6x magnification and an objective lens diameter of 42mm. Ever since 1949, many riflescopes also have adjustable or variable magnification. Such riflescopes usually have their range of magnification marked with two numbers. A variable magnification riflescope, like, for example, 3-9×40 has an adjustable magnification range from 3x to 9x, and an objective lens diameter of 40 mm. Variable power riflescopes are considerably more useful for different types of hunting than those with fixed power. When stalking or drive hunting, a hunter simply varies the magnification of a riflescope to a lesser level which allows them to have a larger field of view, so they acquire their target faster. On the other hand, in the case of the requirement for a longer shot, the hunter simply adjusts the magnification to a greater level and later takes an accurate shot. Such is often the case with alpine and mountain hunting but also with treestand or box blind hunting. Fixed power riflescopes offer the same optical quality at the same magnification as their variable power counterparts, but usually for a cheaper price. Often, their light transmission qualities are better, as they have a lesser number of lenses and usually, they are more lightweight, as well as more compact in comparison to variable power riflescopes. When hunting, a wide field of view is needed, thus a smaller magnification is better than a bigger one. Generally, when hunting, it is not recommended to choose a riflescope with a magnification of less than 4x. The objective lens diameter defines how much light enters the riflescope. Generally, it is one of the main (but not the only) limiting factors for light transmission qualities. On the other hand, the larger the objective lens diameter, the bulkier and heavier the riflescope.
The term “exit pupil” refers to the diameter of the beam of light entering the user’s eye and can be calculated by dividing the diameter of the lens and the magnification of the scope. The size of exit pupil for fixed power riflescopes is usually 7 mm, as this is the maximum range up to which an average adult person’s eye pupil can adjust. Common fixed power hunting 6×42 and 8×56 riflescopes have the exit pupil in the size of exactly 7 (42/6=7, 56/8=7). With an exit pupil of this size, the human eye can gather the most amount of light and consequently allows these riflescopes to have the best light gathering capabilities possible. On the other hand, the size of an exit pupil on variable power riflescopes depends on which magnification they are currently set at. The exit pupil size for these riflescopes is largest at the smallest magnification. Just as with fixed power riflescopes, the best light-gathering capabilities for variable power riflescopes are at the magnification which allows the size of the exit pupil of exactly 7. What sets riflescopes apart from binoculars and spotting scopes is that when the exit pupil with riflescopes is larger than 7, it still has certain benefits – it allows the shooter to acquire optimal aiming eye position faster and easier.
Eye Relief and Fast Focus
Eye relief refers to the distance between the eye and the ocular of the riflescope. It is an important feature as with stronger, Magnum calibers the recoil of the firearm can cause the shooter injuries if the eye relief distance is too short. Modern riflescopes have an eye relief distance of 90 mm on average, as this assures that no damage will be caused to the shooter’s face no matter the firearm caliber and the aggressiveness of the gun recoil. For strong African calibers specifically, riflescopes with an eye relief distance of 120 mm or more are available. Quality riflescopes have a broader range in which the shooter’s eye is in the optimal aiming position and are, when combined with a larger exit pupil, more user friendly. The expression eye–box is used to describe this feature, which simply means that better riflescopes allow greater discrepancy between the shooters aiming eye and the ocular, while still allowing a clear sight picture and accurate aiming. This eye position discrepancy is otherwise measured as the distance from the optimal eye position from the riflescope ocular and the optimal eye position regarding the true riflescope centerline. Modern riflescopes usually allow the shooter to change and adjust the diopter of the riflescope by turning the ocular. This allows the shooter to adjust the sharpness of the reticle or crosshairs. The easiest way to adjust the riflescope to correct the diopter is to aim the riflescope against a solid-colored background (a cloudless sky or a white house wall is quite appropriate) and observe how sharp the picture of the reticle while turning the ocular is. This function of the riflescope is commonly called the fast focus.
Field of View and Light Transmission
Field of view (FOV) of a riflescope means how wide of an area in m (or ft.) you can observe through the riflescope at a distance of 100 m (or 100 yds.). Riflescopes of better quality usually have a greater field of view. Fixed power riflescopes have such a field of view that they cannot be adjusted, and such riflescopes are usually used for stand-hunting as their FOV is narrower. On the other hand, the FOV of variable power riflescopes can be adjusted through the changes in the level of magnification. The greater the difference between the lowest and highest magnification number, or the so-called zoom factor, the greater is the range in which the FOV of such a riflescope can be adjusted. The range of use for such riflescopes is broader, as one can set the riflescope at the lowest setting of magnification for the greatest FOV (for driven hunts, stalking) or the highest magnification setting (for stand hunting or for long-range shooting) or anywhere in between. Today’s riflescopes have a zoom factor of up to 10. Such riflescopes allow, for example, magnification from 1-10x or even from 2,5x all the way up to 25x. In their construction, these riflescopes have a great number of lenses. With more lenses, the light transmission ability of a riflescope suffers as each lens that the light must pass through lessens the strength of light. With modern technologies, materials of exceptional quality, and advanced lens coatings favorable light transmission ability can still be achieved, but that also means that the prices for such riflescopes are relatively high. A good compromise between price, light transmission, and functionality for various types of hunting is offered with riflescopes that have a zoom factor of 4x. Such examples are riflescopes with 3-12x or 2,5–10x magnification, which are today commonly used. It is often said that the main tube diameter (1 inch, 30 mm, or 34 mm – common sizes of modern riflescope’s main tubes) plays an important role in the riflescope’s light transmission ability. Truthfully, the diameter of the main tube plays little role in the light transmission ability, as its main purpose is to serve for a broader adjustment range of the reticle. As with all other optical instruments for hunting use, the most important features for light transmission abilities of the riflescope are the quality of lens glass, the quality of lens coatings, the number of lenses, and the quality of assembly.
The Reticle and the Focal Plane
The reticle, which is the aiming point within the scope, is what sets riflescopes apart from other optical devices. It serves a specific purpose. All other optical devices, such as binoculars, spotting scopes, and telescopes are intended for observing distant objects, while riflescopes are intended for aiming at these objects. Today, most of the riflescopes’ reticles are made so that the reticle is on one of the lenses, and the viewer sees it exactly in the middle of the riflescope’s field of view. In the past, wire crosshairs were common, and they could be adjusted inside the riflescope’s field of view, which in turn also meant they could be outside of the true center of the riflescope. Common European hunting reticle types are shown in Figure 1.
When choosing a reticle type for a hunting riflescope, not only the reticle type but also the focal plane in which the reticle lies in – is important. The light passes through the riflescope’s lenses in such a way that it intersects in two focal plains as shown in Figure 2.
The focal plane closest to the riflescope’s objective (or exit) lens is the front or First Focal Plane (FFP). The focal plane closest to the riflescope’s ocular is the hind or Second Focal Plane (SFP). It is important in which of these two focal planes the reticle lies, as this affects how the reticle reacts during changes in magnification for variable power riflescopes. In the case when the reticle lies in the first focal plane, the reticle crosshairs tend to get thicker and bigger along with the magnification of the target as one adjusts the riflescope (such are most of the older European made riflescopes). With riflescopes that have their reticle in the second focal plane, the reticle crosshairs remain the same thickness, not depending on the level of magnification at which the riflescope is adjusted. At the greatest magnification, the reticle in the second focal plane has fine crosshairs and as such covers only a small part of the target. In the past years, only some US and Japanese-made riflescopes had reticles in the second focal plane. Both types of riflescopes have their advantages and disadvantages. Riflescopes with the reticle in the first focal plane are more robust and have their distances between wires of the crosshairs in the same dimensions no matter the level of magnification one adjusts such riflescopes to. This allows the shooter to judge the distance to the target and to compensate for the bullet drop at further distances using built-in reticle elements (multiple dots, bars) aiming at the target with one of the reticle elements below the center point of the main crosshairs. Judging the distance to a roe deer using a common European reticle type 4 is shown in Figure 3.
A disadvantage of such crosshairs is that they get thicker with an increased level of magnification and can cover a part of the target that is too big. Such riflescopes are also expensive. Modern hunting riflescopes with a reticle in the first focal plane are not common anymore but on the other hand, they are the only choice for tactical and military uses. An advantage of riflescopes with a reticle in the second focal plane is that the thickness of the reticle crosshairs stays the same no matter the magnification level. This allows for extremely accurate aiming. Such riflescopes are considerably cheaper than those with the reticle in the first focal plane. On the other hand, riflescopes with a reticle in the second focal plane have some disadvantages too. Crosshairs can be too thin and not visible enough for shooting in low-light situations (hunting at night), and also, the position of the reticle in the riflescope’s field of view can change during the process of magnifying. Similar problems can occur with riflescopes of lesser quality when adjusting the diopter of the ocular, which can also lead to changes of where the bullet impacts the target. Another problem is that the construction of such riflescopes is far more demanding compared to riflescopes with the reticle in the first focal plane for comparable levels of ruggedness and dependability. European manufacturers were the first who managed to solve these problems and since 1995, upper-class European brands offer riflescopes with the reticle in the second focal plane. European riflescopes of a higher price range are made so that the point of bullet impact on the target varies less than 1 cm at 100 m with changes in magnification. On the other hand – the point of bullet impact on the target can still vary up to 5 cm or more with changes in magnification or diopter adjustments of the ocular for cheaper versions of such riflescopes.
Illuminated Reticles and Crosshairs
With the option of illuminating the reticle in riflescopes, a huge improvement has been made. It used to be so that for hunting in the dark, riflescopes with very thick crosshairs were needed as such design allowed hunters to see them against the target animals, even in complete darkness. For daytime use, such thick crosshairs are not appropriate for accurate aiming at longer distances, as they cover too big of a section of the target. The technologies of reticle illumination changed that forever. With an illuminated reticle it is possible to see even very thin crosshairs against the target in complete darkness. Manufacturers developed more technologies of reticle illumination but in practical hunting situations, only a few types of reticle illumination stand out as most useful. These have just a single illuminated tiny dot or a small, illuminated cross in the middle of the riflescope. It is important to have the possibility of setting the illumination to different levels of brightness – especially to very low levels of brightness. In the case that a large portion of the reticle is illuminated or that the illuminated reticle is too bright, the user’s eye will focus on the illuminated part itself, and not on the target behind. The illumination of the reticle of wide-angle riflescopes – these are riflescopes that offer a large field of view – can somewhat differ from that of other riflescopes. For these riflescopes, it is important to have the possibility of setting the illumination of the reticle to such levels of brightness that the reticle is visible even against the lightest colored of backgrounds as is the snow or the bright sky. A very practical solution is also smart illumination, which means that when the gun is set with the stock on the ground and the barrel pointing up (like when a rifle is in a stored position in a rifle closet), the illumination shuts down automatically. Some systems also automatically shut down the illumination of the reticle after longer periods of inactivity. That helps to save the energy of the batteries needed for the illumination and lengthens the battery lifespan considerably.
Riflescope Turrets for Adjusting the Reticle
Virtually all modern riflescopes offer adjustments of the reticle in such a way that when the scope is mounted on the rifle, the point of aim and the point of bullet have the same impact on the target. Practically no riflescope mounts can be made so precise that the mounted riflescope would require no sighting-in. Usually, fine adjustments are needed. These adjustments are done with two turrets, namely one for windage (horizontal adjustment) and one for elevation (vertical adjustment). The top turret is for adjusting the elevation and the side turret is for adjusting the windage. Hunting riflescopes have turrets protected with caps or covers which protect the turret mechanisms from moisture, dust and other physical damaging factors from outside that could ruin the operating of the mechanisms. The turret cap function is to make the turret mechanism water, fog, and shock-proof. Turrets are, in fact, turnable knobs that are spring-loaded and offer micro-adjustments of the riflescope’s point of aim. Each separate adjustment is a click. Each click moves the bullet impact in a direction engraved on the turret as shown in Figure 4.
Usually, the adjustment direction for moving the bullet impact up is marked on the turret as “UP” and the adjustment direction for moving the bullet impact to the right is marked as “R” (Right). Turrets always have engraved or marked directions on them that show in which way the bullet impact will move on the target. One-click of the turret of European riflescopes usually moves the bullet impact for 1 cm/100 m = for an angle of 1 milliradian (2cm/200 m, 3 cm/300 m…). On the other hand – one click of the turret of US, Japanese and Chinese riflescopes moves the bullet impact for ¼ MOA (Minute Of Angle) that is for the app. 0,69 cm/100 m or app. 1,4 cm/200 m, app. 2,1 cm/300 m…). Bullet impact adjustments using the riflescope’s turret system are intended only for minor corrections. If a riflescope is mounted too far out the true centerline axis, its reticle is under too great of recoil stress, which results in shifting the reticle position between shots. The easiest way to check if a riflescope is correctly mounted and set in or near its true centerline axis is to place a mirror in front of the scope’s objective and observe the reticle. If the reticle and its mirror image can be seen at the same time, one can be certain that the riflescope is correctly mounted and near its true centerline axis. This depends on the quality of the riflescope’s mechanism for adjusting the reticle position if the riflescope’s position will remain unchanged shot after shot and the rifle will shoot true. If the reticle adjusting mechanism is of lesser quality, the changes of bullet impact are noticeable soon after.
Parallax Discrepancy and Systems for Adjusting the Parallax
Parallax discrepancy is a concept that is often talked about when discussing riflescopes, but hunters and shooters still know little about it and the reasons behind it. As it was described earlier – each riflescope has two focal planes. There are also two focal points where light rays intersect outside the riflescope’s construction. One such focal point is the eye position behind the ocular and the other is in the position of the target as shown in Figure 5.
Most hunting riflescopes are factory set to compensate for parallax and focus for an optimum distance of 100 m. At this distance, the target image is sharpest and what is even more important: the reticle is always in the same position on the target regardless of how far the shooter’s aiming eye is outside the riflescope optical axis. At all other distances, parallax discrepancy occurs, and adjustment is needed as aiming eye position outside the optical axis of the riflescope causes the reticle to move on the target. Parallax discrepancy is especially obvious and causes missed shots at shorter distances and at higher magnifications. Because of the latter, it is recommended to use riflescopes that allow adjustability of the parallax on rimfire and small-caliber rifles. At magnifications under 10x, parallax compensation is not needed, thus such riflescopes almost never have systems for adjusting the parallax. On the other hand, riflescopes with greater magnification levels usually have systems for adjusting the parallax that moves the position of the riflescope lenses in such a way that the distance of the focal point on the target changes. Most common systems are with a turnable ring on the objective – AO (Adjustable Objective) or with an extra turnable side turret knob on the left – SF (Side Focus). For general hunting use, it is seldom required to use riflescopes with a magnification greater than 10x, and it can also be stressful, as well as time-consuming for an average hunter to adjust the parallax before each shot. Similar to other riflescope functions, this also stands true for parallax adjustability: quality riflescopes have a smaller parallax discrepancy, and those of lesser quality have a greater parallax discrepancy.
Concluding Thoughts and Recommendations
Riflescope is an essential tool for a hunter and it greatly contributes to the ethical harvesting of game animals. Because of the latter, choosing the right riflescope is important and it mostly depends on one’s hunting methods. The quality of the riflescope’s construction is important as this affects the reliability of the riflescope and it means that the position of the crosshairs does not shift from shot to shot. It must enable the hunter to make an accurate shot even in low light conditions but also to give the hunter the confidence to make accurate shots in stressful situations. In general, for various types of hunting, the following types of riflescopes are recommended:
- Driven hunts: 1-4 x 24; 1-5 x 24; 1-6 x 24; 1-8 x 24; 1-10 x 24 with an illuminated dot or a small reticle that can be set to high levels of brightness (daytime use)
- Stalking: 1,5-6 x 42; 1,5-8 x 24; 1,5/1,7-10 x 42; 2-8 x 42; 3-9 x 40
- Mountain and alpine hunting: 2,5-15 x 44; 3-15 x 50; 3-18 x 50; 4-16 x 50
- Stand or box blind hunting in low light conditions: 8 x 56; 2,5-10 x 56; 3-12 x 56; 2,5-15x 56 with illuminated crosshair reticle
- Multi-purpose riflescopes: 2-12 x 50; 2,5–10 x 50; 3-9 x 50; 3-12 x 50
After choosing the right riflescope one must choose the quality mounting hardware as well. It is necessary that one practices with the setup rifle and takes enough practice shots on the target before going hunting, as only this will provide the needed confidence. As hunters, we strive towards fast humane kills. We owe that to our quarry. Only with practice and correct quality setup equipment can we prevent the wounding of game animals.
Source and author: Teodor Štimec, www.optics-trade.eu