Magnification... eye relief... field of view... light transmittance... Which is most important when choosing a best rifle scope? That depends on your shooting activity. Learn how to choose the best scope here.
How to choose the best rifle scope? Scope manufacturers strive to offer a scope for almost every conceivable shooting and hunting activity.
Scopes are available with a variety of magnifications, reticles, click adjustments, objective lens diameters, scope tube diameters, finishes, features, accessories, and . . . the list goes on.
There are so many options available for rifle scopes. As you may have discovered, there are hundreds of scope models available from dozens of manufacturers.
But no particular scope is ideal for every shooting activity and situation. It is up to you to order the perfect rifle scope for your situation.
But how will you ever sort through so many options?
To make your choice easier, scope selection can be separated into two areas: optical performance and features.
Section 1: Optical Performance
Scopes have become popular because they have advantages over sights. Aiming is easier with a scope than with open sights.
Targets tend to hide behind the front sight. There is not a front sight to hide the target when aiming with a scope. The target is visible around the reticle aiming point because the scope reticle appears to be imposed directly on the target.
A shooter can aim carefully without eyestrain while sighting with a scope because he or she does not have to rapidly switch focus between the scope's reticle and the target while aiming with a scope.
Also, a quality scope allows the shooter see better in low light conditions than sights.
A scope will direct the ambient light rays that form the target image into the pupil of the shooter's eye where the rays can do some good.
That is more than sights will do. In fact, a front sight, being directly between the target and the shooter's aiming eye, will block much of the light from the target. This could make the target seem to disappear in low light conditions.
But the most obvious advantage is magnification.
Magnification is usually the first specification a shooter considers when shopping for a best rifle scope and it is one of the first criteria listed on scope specifications.
With rifle scopes, as with other optical devices, magnification power is simply expressed as "power".
Power is indicated with the scope specifications by the letter "X". The digit or digits before the "X" indicate the scope's power. (The digits after the "X" indicate the scope's objective lensdiameter in millimeters).
Some scopes have fixed power. Their power cannot be changed by the shooter.
On the other hand, variable power scopes allow the shooter to adjust the scope's magnification within its power range to match the current situation.
Variable power is expressed with a hyphen to indicate the power range (from lowest to highest) followed by the letter "X". (For example: 3-9X).
Not only does magnification make the target seem closer but, combined with precise windage and elevation adjustments, increases shooter confidence.
With adequate magnification a shooter does not merely aim at the target. No; A shooter can choose where to aim on the target and, with a precisely zeroed scope, can hit where aiming.
Well, with all that going for scopes, why not just order the scope with the highest magnification, the finest reticle, and the largest objective lens?
Magnification is an important consideration when choosing a best rifle scope. That does not mean the highest power available is the best option.
Other optical parameters such as field of view, light transmission, and eye relief decrease as magnification increases. These criteria may be even more important than magnification in some situations.
Thicket / Jungle
Deer / Bear
Deer / Sheep
Deer / Bison
Varmint / Predator
Varmint / Predator
Too much magnification can actually be detrimental in certain situations.
So why do scope manufacturer's offer scopes with extreme magnification - scopes with 25X, 35X, even 45X?
Because extreme magnification is acceptable in certain target shooting activities. Target shooters normally have time to set up and aim carefully.
Since the rifles used in many target shooting activities have light recoil, eye relief is usually not a major concern.
Many shooting ranges have artificial lighting for early morning or late evening shooting. The shooter knows the location and range of the targets - no searching for targets through the narrow FOV of a high power scope.
Printed targets contrast with the surroundings and have definite aiming points.
They often shoot from steady, elevated benches over clear, level ground with an unobstructed view of targets - targets that are not trying to get away.
And competition shooters do not have to be concerned about being attacked by their target as do dangerous game hunters.
Even target shooting conducted at outdoor shooting ranges is much different than field hunting.
Extreme magnification that is intolerable in hunting situations may be normal for some range situations.
2. Field Of View
Consider field of view. Field of view (FOV) is the width of the area that is observable through the scope.
FOV for rifle scopes is commonly expressed in feet of width at 100 yards distance (or meters of width at 100 meters).
Because FOV is an angular measurement, it widens in direct proportion to the viewing range. The FOV at 100 yards actually means FOV per 100 yards of viewing distance.
All scopes have a limited field of view. Limited field of view is a major disadvantage inherent with optical devices. A shooter cannot see anything outside the FOV. A narrow FOV makes finding a visually spotted target with a scope difficult or tracking a moving target nearly impossible.
A wide FOV is desirable. Wide FOV helps a hunter sight game with the scope before the game gets away - or before the game gets the hunter.
What does field of view have to do with magnification?
Magnification adversely affects FOV. The higher magnification, the narrower FOV.
The lower the power, the wider the FOV. A scope cannot have both high magnification and wide FOV. The FOV of variable power scopes can be widen only so much by decreasing power.
High magnification or wide FOV? You must decide which is more important for the intended shooting activity and conditions before ordering a scope.
3. Exit Pupil
Magnification also affects the size of a scope's exit pupil.
Exit pupil diameter is not a physical dimension. Rather, it is an optical dimension formed by the light beam emitted from the scope toward the shooter's eye. The larger the exit pupil, the wider the beam of light directed to the shooter's eye.
Exit pupil is often listed with other scope specifications.
A scope for hunting in low light conditions should have about a 5mm exit pupil. (A 5mm scope exit pupil closely matches the 5mm dilation of a normal human eye pupil in low light.)
A scope with an exit pupil less than 5mm will not be a good choice for hunting in the early morning or late evening. Such a scope will work just fine during the day when the shooter's eye pupils have constricted to as small as 2mm due to bright light anyway.
Exit pupil is influenced by a scope's magnification and its objective lens diameter. The objective lens is the closest lens to the target; the first lens of a series of lenses.
The objective lens - the farthest lens from the shooter - affects the diameter of beam of light exiting the scope toward the shooter's eye.
Exit pupil (in millimeters) is calculated by the dividing a scope's objective lens diameter by its magnification. (Scope objective lens diameter is usually listed immediate after its power and expressed in millimeters.)
Objective lens diameter (in mm) divided by power = exit pupil (in mm)
- 30mm ÷ 3 power = 10mm
- 30mm ÷ 6 power = 5mm
- 40mm ÷ 20 power = 2mm
- 50mm ÷ 10 power = 5mm
We can conclude from the equation that, for any objective lens diameter:
- the lower the magnification, the wider the exit pupil; and
- the higher the magnification, the narrower the exit pupil will be.
And, for any magnification:
- the wider the objective lens diameter, the wider the exit pupil; and
- the narrower the objective lens diameter, the narrower the exit pupil will be.
Therefore, a large objective lens is necessary on a high power scope just to have a sufficient exit pupil for aiming in low light conditions.
Essentially, the size of the objective lens determines how much light enters and magnification determines the size of the light column that exits the ocular lens toward the shooter's eye.
Exit pupil merely describes the size of the light disk that reaches the shooter's eye. Exit pupil does not influence the brightness of the light beam emitted from the scope. The brightness of the light disk transmitted through the scope is influenced by lens quality - particularly lens coatings.
4. Lens Coatings
In addition to exit pupil size, lens quality also affects how well a scope delivers light to the shooter's eye.
A lens would ideally transmit all the light that reaches it surface.
However, no lens is perfect. Reflection, refraction, aberrations, absorption, and glare reduce the light transmittance of every lens to some degree.
Each lens within a scope has both front side and reverse side reflection.
Light that is reflected is light not transmitted to the shooter's eye.
Even simple scopes contain several lenses. Each of those lenses reduce light transmission a bit.
Reflection through a low-quality, multi-lens scope could reduce light transmittance as much as 50%.
Most modern scopes have some form of anti-reflective lens coating to reduce reflection, thus, increase light transmittance to the shooter's eye.
Good scopes have fully coated lenses or even multi-coatedlenses.
Quality scopes have fully multi-coated lenses. Scopes with fully multi-coated lenses allow 95% of the light to be transmitted to the shooter's eye.
Order a scope with fully multi-coated lenses if you anticipate hunting early morning or late evening.
sufficient exit pupil + coated lenses = good light transmittance
5. Objective Lens Diameter
As described above, exit pupil size is a major factor that affects scope light transmission and that exit pupil is determined by objective lens diameter and magnification.
A larger objective lens makes a larger exit pupil for any power level. A large objective lens is necessary on a high power scope just to have a sufficient exit pupil to shoot in low light.
You could order a scope with a large objective lens from the start if you plan to hunt in low light. Forty millimeters or larger.
So why not order a scope with the largest objective lens available? One that has a large objective lens out of proportion to its power. Because a scope with a large objective lens must often be mounted too high for the shooter to get a solid stockweld.
A large objective lens must be enclosed within a large objective lens bell.
Since there must be space between the objective lens bell and the top of the barrel, a scope with a large objective lens must be mounted high to clear the barrel.
With a scope mounted too high, the shooter must raise his cheek off the buttstock comb to align his eye with the exit pupil.
If the shooter's eye is not in the same position relative to the scope it was when the scope was zeroed, parallax error will occur.
Also, since the shooter's head may not recoil with the rifle without a solid stockweld, eye relief becomes an issue.
An extremely large objective lens larger is appropriate only if you will be using high magnification to shoot in low light conditions.
If you plan to shoot in low light conditions with high magnification, by all means, order a scope with an extremely large objective lens.
But do not order a scope with an extremely large objective lens just for the sake of having a scope with an extremely large objective lens.
6. Eye Relief
Eye relief is the distance the viewer's eye must be from the ocular lens to allow the viewer to see the whole exit pupil.
The viewer will see a dark area around the perimeter of the field of view if the viewer's eye is closer than the minimum eye relief distance or farther than the maximum.
A reasonably long eye relief is desirable in rifle scopes; longer than with most other optical devices.
Eye relief must be sufficient to allow the rifle to recoil against the shooter's shoulder without allowing the rim of the eyepiece to gash the shooter's eyebrow.
The heavier the recoil, the longer the eye relief must be. Even light recoiling rifles should have scopes with at least three inches of eye relief. Medium recoil rifles at least 3+1/2 inches of eye relief. And heavy recoil rifles, at least four inches.
The problem is that eye relief decreases as magnification increases. Increase the power of a variable power scope and you'll decrease eye relief. Magnification must be low enough to allow sufficient eye relief on heavy recoil rifles.
Lightweight, high-power rifles and high magnification scopes, with their short eye relief, are not compatible.
Scope manufacturers can actually make scopes with much longer eye relief. (Some make handgun scopes with extended eye relief.)
So why don't they make rifle scopes with longer eye relief?
Magnification is one reason as previously stated. Another reason is field of view (FOV). Increased eye relief results in reduced FOV. FOV suffers if eye relief is extended beyond what is needed based on intensity of recoil.
Do not order a scope with a 3/4-inch main tube for a centerfire rifle even if you can find bases and rings to mount it.
Scopes with 3/4-inch scope tubes are designed specifically for air rifles and rimfire rifles with very light recoil.
Such scopes are designed with a short eye relief - so short that eyepiece could strike the shooter's eye during recoil if they were mounted on a centerfire rifle.
High magnification or long eye relief or wide FOV? You cannot get all three in the same scope.
A scope will magnify anything within its field of view including something you do not want to be magnified - mirage.
Mirage is image blurring and distortion caused by rising heat waves.
Mirage will cause the target appear to distort with the breeze. Mirage is present to some extent wherever the surface is warmer than the air above it.
Mirage is most noticeable when the line of sight is parallel to and close to the surface.
Also, depth of mirage increases as range to the target increases.
The target must be viewed through the mirage. Because mirage is between the scope and the target, magnification will magnify the mirage to a greater extent than it magnifies the target. The higher the scopes power, the more intense the mirage will seem.
The view through a low power scope will be less distorted by mirage than the view through a high power scope.
You should reconsider ordering a high power scope if you anticipate frequently shooting over a hot, flat surface.
Tremor is something else you do not want magnified. Whenever a shooter grasps a firearm to shoot, a certain mount of unintentional movement is imparted on the firearm by the shooter. Even a shooting rest may not eliminate all tremor.
Tremor is noticed in two ways - the inability to discern target details and the drifting of the reticle about the intended aiming point.
Scope magnification exaggerates tremoring.
A drifting reticle could frustrate the shooter so much that the shooter may just yank the trigger when the reticle finally does drift across the aiming point just to get the shot off.
Rifles with high-magnification scopes should be supported by a rest to shoot.
Do not order a high power scope if your shooting will be done offhand or from uneven terrain.
Section 2: Rifle Scope Features
Modern rifle scopes are available with a variety of features. Which features should your scope have? That depends on your shooting activity. Learn how to choose the best scope for your shooting activity.
Obviously a rifle scope's optical performance will help you to see targets better. But you are looking for a rifle scope to help you aim as well.
Scopes have features to help you to sight in and aim at targets also.
Features such as reticles, internal windage click adjustments, and elevation click adjustments. Without such features a rifle scope would merely be a telescope that can be attached to a rifle.
Optional features such as parallax adjustments, variable-power, optical rangefinders, and bullet drop compensators are available with some models to further increase scope utility.
No single scope is ideal for every shooting activity. A particular scope may fit one shooting activity well, be a compromise for some activities, and be unsuitable for others.
In addition to optical performance (as explained above), you must decide which scope features best serve your shooting activity.
With so many features available, how do you choose the best rifle scope? This part describes some important options you should consider before ordering a scope.
1. Fixed Or Variable-Power
Rifle scopes have either fixed-power or variable-power.
The magnification of a fixed-power scope is set in the factory and cannot be changed by the shooter. Its power is listed with its specifications and is indicated with the letter "X" (for example: 10X).
The magnification of a variable-power scope, on the other hand, is adjustable within its power range by the shooter. The power range of a variable-power scope is shown with a hyphen between minimum and maximum power and is also indicated by the letter "X" (for example: 3-9X).
Variable-power allows shooters to adjust magnification as well as the other parameters magnification affects - field of view (FOV), exit pupildiameter, and eye relief. The shooter can adjust the magnification of a variable-power scope to match the shooting activity and the current conditions.
The lowest power setting provides the widest field of view for making quick, unexpected shots at close range and for tracking running game.
A hunter can carry a rifle with the scope power set at low power to take quick shots at close range then crank up the power to take slow, deliberate shots at longer ranges.
The wider FOV of low power settings helps to locate a target in the scope previously seen visually before zooming in to take a precise shot.
Finally, the hunter could decrease power again if the distortion caused by mirage becomes a problem.
Due to their versatility, variable-power scopes far outsell fixed-power scopes. So why even make fixed-power scopes?
Because some shooters still prefer fixed-power scopes. These shooters prefer fixed-power scopes because they are generally lighter, shorter, more durable, more reliable, and less expensive than variable-power scopes of similar quality.
Fixed-power scopes have fewer parts because they do not have a power adjustment system. There are fewer parts to make and install during manufacturing and fewer parts to break or wear out during use.
Many competition shooters prefer fixed-power scopes because not being able to adjust magnification, FOV, and exit pupil is more acceptable to them than even the slightest change in zero that may accompany power changes.
Besides, many owners of variable-power scopes set the power at one power level then rarely change it anyway.
The power adjustment mechanism adds weight, complexity, and cost, therefore, variable-power scopes are generally longer, heavier, and more expensive than fixed-power scopes.
The extra length is required to install the power adjustment tube inside the main scope tube.
The power ring of a variable power scope is an external control linked to an internal mechanism.
Not only does the power change mechanism increase complexity, but a variable-power scope must have a power ring groove cut through its main tube.
The power ring groove is the weakest area of a variable-power scope tube. Also, the power ring is an area where moisture can seep in.
The main tube of a fixed-power scope does not have a power ring groove or any of the potential problems of a power ring groove.
But do not be down on modern variable-power scopes. No. Quality, variable-power scopes are very reliable despite all their potential problems.
The zero shift as power is changed on quality variable scopes is almost indiscernible. Modern scopes rarely leak around the power change mechanism (or anywhere else) anyway.
The certain versatility of a variable-power scope overshadows its potential problems.
Fixed-power or variable-power? You decide.
The primary purpose of a rifle scope is to assist the shooter with aiming the rifle. Magnification will make the target appear larger, but aiming is the primary purpose of a rifle scope.
With that in mind, the scope manufacturers continue to improve and enhance reticles.
The reticle of a rifle scope is aiming reference within a scope. It is the presence of a reticle that distinguishes a telescopic sight from a telescope.
Reticles have evolved from simple crosshairs. Thick crosshairs were easy for the shooter's eye to find for quick shots at close range. But thick crosshairs could also obscure small targets at long range.
On the other hand, fine crosshairs were useful for taking deliberate shots at stationary targets but blend with shadows and other dark backgrounds or disappear in low light making aiming difficult.
Dual thickness crosshairs combine thick crosshairs and thin crosshairs in one reticle.
The thick sections that comprise the outer 9/10th or so of the crosshairs are available to make quick shots at close range or into low light.
The middle 1/10th is thin for taking slow, precise shots.
Although the dual thickness crosshair reticle was introduced in 1962, it is still popular because of its uncluttered efficiency and intuitiveness.
Dual thickness crosshairs are known by several trade names depending on the brand of scope including "Duplex", "Truplex", "Dual-X", "Multiplex", and "Multi-X".
Center circle and center diamond reticles are basically dual thickness crosshair reticles with a circle or an open diamond around the thin sections of the crosshairs.
The circle or diamond draws the shooter's eye to the center of the FOV for quick shots and retains thin sections of crosshairs for precise shooting.
The center dot reticle, also called an MOA dot reticle, is sort of like the opposite of the dual thickness crosshair reticle. It consists of a center dot that appears to be suspended at the intersection of thin crosshairs. The size of the center dot varies between scope models.
Center dots subtend as small as 1/8 minute-of-angle (MOA) and up to one MOA depending on the model. (One MOA is about one inch per 100 yards of range.)
Some shooters like the one MOA dot because this reticle facilitates quick shots at close range and believe that 1/8-MOA and even the 1/4-MOA dots are too small.
Others like the 1/8-MOA dot for long range shooting. They believe even a 1/4-MOA dot obscures small targets.
One dot size does not please everyone. Before you order a center dot reticle, have an idea of what kind of shooting you will be doing; then order the best size of dot accordingly.
Tactical reticles have become popular because they are not just aiming reticles. In addition to aiming, shooters can use mil reticles to estimate target range, adjust hold-over or hold-under, apply wind correction, lead moving targets, and correct for inclination or declination.
Tactical reticles feature reference marks imposed on the vertical and horizontal crosshairs based on the milliradian (mil) measurement system.
(A milliradian is angular divergence measured with any unit of length measurement at a distance of 1000 times that unit. For example, 1 inch of width measured at 1000 inches of distance is a milliradian as is one foot of width measured at 1000 feet, 1 yard at 1000 yards, and so on.)
Although frequently called mil-dot reticles, tactical reticles may display mils as circles or lines as well as dots depending on the scope model.
Tactical reticles are popular with varmint hunters and target shooters as well as law enforcement and military snipers.
Black reticles are indiscernible in low light against dark targets. Illuminated reticles solve this problem.
Scopes with illuminated reticles use battery power to make the reticle glow either red or green.
The reticle may be a dot, circle, or tactical reticle. These scopes do not amplify light as night-vision scopes do; they only illuminate the reticle to make it stand out from dark backgrounds.
3. Integral Rangefinders
Optical rangefinders integrated within scopes require the shooter to estimate the size of the target then bracket the target between the two horizontal lines.
The estimated range is read within the scope field of view adjacent to the appropriate horizontal line or one the power ring.
If the target is a game animal, optical rangefinders are only reliable if the animal is standard-sized, exposes itself clearly, and stands broadside long enough to be bracketed.
The estimated range will be wrong if the animal is not standard-sized or does not cooperate with the hunter.
Unlike optical rangefinders, laser rangefinders (LRFs) do not require the animal to be a standard size or to be entirely cooperative. Plus, laser rangefinders are far more accurate than scope-based optical rangefinders.
However, handheld laser rangefinders are difficult to hold steady while taking readings.
Wouldn't it be convenient if you could steady a laser rangefinder like you do while aiming a rifle?
Wouldn't it be even better if you did not have to set the laser rangefinder aside then scramble to find the target in the scope also.
Well, laser rangefinding rifle scopes incorporate a laser rangefinder within a rifle scope. Now, a shooter can aim at a target and range it simultaneously with a laser rifle scope while steadying the rifle on a rest.
4. Trajectory Compensators
Using a rangefinder, hunters can measure whether or not a game animal is within point blank range or even effective range.
Some hunters may want to place their shot precisely although the game is within point blank range. In either case, a hunter must compensate for bullet trajectory to place the shot for a clean kill.
The hold-over / hold-under method and the click-up / click-down method are two methods used to compensate for trajectory when the target is at a range other than the zero range.
The hold-over method requires the shooter to aim above the vital zone the distance the bullet will drop at that range. Ballistic reticles are available with some scopes as an aid to using the hold-over method.
Ballistic reticles have additional reference points, circles, or lines along the lower half of the vertical crosshair.
The shooter aims using whichever reference point, circle, or line closest represents the trajectory at that range.
The farther the target, the lower the reference line the shooter must use.
The scope instruction manual indicates the subtension each line represents relative to the horizontal crosshair.
The reference lines rarely match trajectory perfectly, but using a reference line is better than merely visualizing hold-over.
The tactical mil reticle is one example of a ballistic reticle.
The click-up method of trajectory compensation is more precise than the hold-over method but takes longer to set up.
Trajectory compensation is achieved when using the click-up method by adjusting the elevation dial the number of clicks appropriate for the range to compensate for bullet drop.
Using the click-up method, you can aim spot on after the elevation dial is set correctly.
Some optical rangefinding scopes include a set of interchangeable trajectory compensating scales that slip onto the elevation adjustment turret.
The scales place the click adjustments from a trajectory table directly on the elevation turret.
The ring with the scale that represents the trajectory best is installed onto the elevation turret after the rifle is zeroed.
While hunting, the hunter refers to the scale installed on the elevation turret to dial in the trajectory correction.
Then the hunter can aim directly at the game. The hunter has actually rezeroed the rifle to the current shooting distance.
Some laser rangefinding scopes rely on the click-up method for trajectory compensation.
Other laser rifle scopes provide ballistic reticles. However, the latest laser scopes have internal ballistic computers.
The shooter must program the scope with the trajectory. After programmed, the computer automatically repositions the electronic reticle to compensate for trajectory based on the range measured by the LRF.
The ballistic computer also factors declination and inclination angles into the trajectory compensation.
5. Click Adjustments
Elevation and windage on modern scopes are adjusted internally.
Internal adjustments help a shooter precisely zero a scope to the rifle it is mounted on. In addition, elevation adjustments also provide a way for shooters who use the click-up method to compensate for trajectory.
The click adjustments may be provided by target knobs that protrude from the scope main tube or by dials that are nearly flush with the tube depending on the model of scope.
Dials are protected by removable caps to prevent damage. Dials require a coin or screwdriver to make adjustments. Target knobs can be turned with fingers.
Knobs may or may not be protected by caps. Knobs on certain scope models have a locking ring that tightens to prevent the knob from being turned inadvertently.
Most shooters who use the click-up method of trajectory compensation prefer adjustment knobs.
The click reference lines on knobs can be seen by the shooter while in a shooting position and adjustments can be made with minimum disturbance from the shooting position.
However, knobs are more likely than dials to be damaged by boulders or snagged in brush while hunting.
Therefore, target knobs are generally preferred by competition shooters and varmint hunters while dials are generally preferred by big game hunters.
You will want to be sure whether or not you have adjusted the correct number of clicks.
Adjustment clicks must be discernible tactilely, audibly, and visually.
Target knobs provide visual confirmation that the correct number of clicks actually were made. However, the reference lines on knobs will not be visible in low light.
Therefore, clicks must be discernible by feel including with cold fingers or through thick gloves.
The click value indicates how far the bullet point-of-impact should move at the prescribed range.
The actual distance each click value moves bullet point-of-impact is directly proportional to the range of the target.
The farther the target, the more each click will move the point-of-impact on the target.
The most common click adjustment value is 1/4-inch at 100 yards distance. (That is actually 1/4-inch per 100 yards of range.)
Other click values are 1/2-inch and 1/8-inch at 100 yards (per 100 yards, actually).
Occasionally clicks increments are expressed in minutes-of-angle (MOA) or some fraction of MOA. One MOA is 1.047 inches at 100 yards - very close to 1 inch at 100 yards.
So for practical purposes, 1/4-MOA clicks can be considered 1/4-inch clicks.
Scopes with 1/8-inch click adjustments can be zeroed more precisely than scopes with 1/4-inch clicks.
However, such fine clicks many be inconvenient for shooters who use the click-up method of trajectory compensation.
Twice as many 1/8-inch clicks are required as 1/4-inch clicks to compensate for trajectory at any range.
The full range of 1/8-inch clicks may not be sufficient to compensate for trajectory at extremely long-ranges - just where trajectory compensation is most needed.
6. Tube Diameter
Rifle scope main tubes are usually either 1-inch or 30mm diameter.
Rifle scopes with 3/4-inch diameter tubes are designed for air rifles or rimfire rifles.
Scopes with other tube diameters, such as 27mm, 34mm, and 35mm, are rare.
Thirty millimeter main tubes (about 1+3/16-inch) are slightly larger than 1-inch tubes.
Thirty millimeter tubes of the same wall thickness have space for a few more internal windage and elevation click adjustments than 1-inch tubes.
The 30mm tubes are also slightly more rigid than 1-inch tubes of the same wall thickness.
7. Objective Lens Diameter
The larger the objective lens diameter, the larger the exit pupil at any magnification.
Hunters who intend to hunt in low light conditions should order a scope that has an exit pupil no smaller than 5mm.
Exit pupil is normally listed with the scope specifications. If the exit pupil is not listed, divide the objective lens diameter in millimeters by scope power. Use the lowest power setting in this equation if the scope has variable-power.
A large objective lens is necessary on high magnification scopes just to have a sufficient exit pupil to shoot in low light conditions.
So why not just order a scope with an extremely large objective lens even if you do not plan to shoot in low light?
Because a scope with a large objective lens must be mounted high to clear the top of the barrel.
There must be at least a 1/8-inch space between the objective lens bell and the barrel.
With a scope mounted too high, your cheek may not be supported by the buttstock comb while aiming, causing inconsistent eye position.
Parallax error will occur if the your eye is not in the same position that it was relative to the scope when the scope was zeroed.
Do not order a scope with a large objective lens just to have a scope with a large objective lens.
You should order a scope with an extremely large objective lens - larger than 40mm - only if you plan to shoot in low light with a high magnification scope.
8. Parallax Adjustment
Parallax is the perceived relative movement between two separate stationary objects at different distances as viewed by an observer from various locations.
Scope parallax refers to the perceived drifting of either the target image or the reticle whenever the shooter's eye position changes vertically or laterally while aiming with a scope.
If the target is stationary and the scope is steady, perceived movement of the reticle or target may be due to shooter eye movement. Parallax can cause shot placement error.
Parallax error is present whenever the target image and reticle are not on the same focal plane and the shooter's eye is not consistently realigned with the scope's exit pupil before each shot.
Ideally, the target image would be located on the reticle. The reticle and target image will appear to be conjoined in this case. There will be no reticle drifting no matter where the shooter positions his eye within the boundary of the exit pupil.
The location of the target's image within the length of the scope depends on the real target's distance from the scope's objective lens.
Just as the range to the target varies between different shooting situations, so will the target image within the scope.
As a result, the current target's range rarely causes the image focal plane to coincide with the reticle position within the length of the scope.
Moving closer to or farther from target to get the focal plane to coincide with the reticle is rarely practical. So shooters must either optically adjust the focal plane to coincide with the reticle or simply accept the possibility of parallax error.
Adjusting the focal plane to the reticle requires the scope to have a parallax adjustment mechanism.
Not all scopes have a parallax adjustment mechanism. Many scopes have parallax set at the factory for some intermediate range depending on the expected use of the scope.
Parallax on these scopes cannot be adjusted by the shooter. The factory set range is typically 50 yards for scopes intended for air rifles and .22 rimfire rifles and 100 yards for scopes intended for big game hunting.
Some parallax error is acceptable in big game hunting scopes because within 200 yards the maximum parallax error does not exceed the vital area of big game animals.
However, competition riflemen, varmint hunters, and other shooters who regularly shoot beyond 200 yards generally prefer scopes with adjustable parallax.
Parallax adjustment allows the shooter to position focal plane within the scope to coincide with the reticle's position.
Parallax can be readjusted each time the range changes. Scopes with parallax adjustment have either an adjustable objective lens or a side knob parallax adjustment mechanism.
The objective lens bell is twisted to eliminate parallax with an adjustable objective (AO) lens system.
Reference marks around the objective bell represent various ranges to help the shooter make a rough adjustment.
If a rest is available, fine parallax adjustment is done by steadying the rifle and viewing through the scope at the target while twisting the objective bell.
Parallax has been eliminated when the objective lens has been twisted to a position where no target to reticle drifting is noticed whenever the shooter makes slight head repositions.
Scopes with a side knob parallax adjustment system include a knob on the left side of the main tube adjacent the elevation adjustment.
The knob also has reference marks to help make rough parallax adjustments. The rifle must also be steadied on a rest while viewing through the scope to make fine adjustments.
The adjustable objective lens system is easier to learn and is sturdier than the side knob adjustment system.
However, because the adjustable objective lens is at the opposite end of scope from the shooter, the shooter cannot view the range reference marks on the surface of the objective bell while in the prone shooting position.
On the other hand, the reference marks of the side knob can be viewed from any shooting position.
Also, a side knob is easier to reach while viewing through the scope to make fine parallax adjustments than an AO, especially with long scopes.
Now let's consider scope outer surface finishes.
Nearly all models of scopes are available with gloss (shiny) black or matte (flat) black anodized finishes.
Some models are available with "silver" finishes. Maybe you want a scope finish that matches your rifle receiver - gloss black to match a black oxide rifle finish, matte black to match a parkerized finish, or silver to match stainless steel.
Scopes with silver finishes are normally mounted only on competition rifles because camouflage is not an issue with competition rifles.
Some models of scopes are available with camouflage finishes if you really are concerned about camouflage.
You know what shooting activity you intend to participate in before you order a scope. You know the environment you will be in and the method you will use. And you know what rifle and cartridge you will use. Now you just have to order a scope that matches.
There are so many rifle scope models with countless features currently on the market.
Order a scope with enough power but not too much. The scope you order should have only slightly more magnification than the cartridge effective range requires. Anymore magnification could be a liability.
Remember, a scope is an aiming aid; not a scanning or spotting aid. Order enough scope power to aim with but use a binocular or a spotting scope to scan for targets.
Besides, if you use a scope for scanning you will also be aiming - aiming at something you do not intend to shoot.
Only you can decide which scope to order. Uninformed shoppers order scopes with too much magnification. Consider yourself informed.
Choosing the best rifle scope for your shooting activity can be difficult. Perhaps this article has helped you sort through some of the options to decide which scope to order.