Rifle Scope Objective Lens Sizes Explained: 32mm, 40mm, 42mm, 44mm, 50mm & 56mm

The objective lens is the large front lens of a rifle scope. Its diameter is one of the most visible differences between scope models, with 32mm, 40mm, 42mm, 44mm, 50mm, and 56mm being common sizes.

But how much does objective size actually matter? Is a 50mm scope brighter than a 40mm scope? Is a 56mm objective worth the additional size and weight? Does a larger objective require higher scope rings? And what objective size makes the most sense for a hunting rifle versus a long-range rifle?

The answer depends on more than the diameter of the front lens. Objective size works together with magnification to determine exit pupil, while glass quality, coatings, optical design, light transmission, mounting height, scope weight, and the intended use of the rifle all affect the practical performance of the optic.

A larger objective can provide a meaningful advantage in certain applications, particularly when high magnification is used in low light. But bigger is not automatically better. For many hunting rifles, a smaller objective provides a better overall balance of optical performance, weight, mounting height, and handling.

What Does Objective Lens Size Mean on a Rifle Scope?

The objective lens is the front lens of a rifle scope. The objective size refers to the approximate diameter of that lens in millimeters.

For example, a scope described as a 40mm objective has a front objective lens approximately 40mm in diameter. A 50mm scope has an objective approximately 50mm in diameter.

Common rifle scope objective sizes include:

These categories should not be treated as rigid classifications. Scope manufacturers choose objective sizes as part of an overall optical design, and two scopes with the same objective diameter can have very different optical characteristics.

Why Does Objective Lens Size Matter?

Objective diameter matters primarily because it establishes the amount of light that can enter the scope's optical system and, in combination with magnification, influences the size of the exit pupil.

However, the amount of light entering the objective is not the same thing as the brightness of the image delivered to your eye. Light must pass through the entire optical system, and the quality of the glass, lens coatings, optical design, and other factors affect how efficiently that light is transmitted.

Objective size also affects the physical design of the scope. Increasing objective diameter generally requires a larger objective bell and can increase overall size and weight. On some rifles, the larger bell can also influence the mounting height required to obtain adequate clearance above the barrel.

Consequently, objective size is a tradeoff rather than a simple measure of scope quality.

What Is Exit Pupil?

Exit pupil is the diameter of the beam of light leaving the scope's eyepiece and entering the shooter's eye. It is one of the most useful measurements for understanding how objective diameter and magnification interact.

The formula is straightforward:

Exit Pupil = Objective Diameter ÷ Magnification

For example, a 50mm objective at 10x magnification produces a 5mm exit pupil:

50mm ÷ 10 = 5mm

A 40mm objective at the same 10x magnification produces a 4mm exit pupil:

40mm ÷ 10 = 4mm

Increasing magnification reduces exit pupil. Increasing objective diameter increases exit pupil at the same magnification.

Why Does Exit Pupil Matter?

The human eye's pupil changes size according to ambient light. In bright daylight it becomes relatively small, while in darkness it can become substantially larger.

If the scope's exit pupil is larger than the shooter's eye pupil, the eye cannot make use of the entire diameter of the available light beam. If the exit pupil becomes smaller than the eye pupil, eye positioning becomes more critical because the eye has less room to move while maintaining the complete image.

This is particularly relevant at high magnification and in low light. A larger objective can help maintain a useful exit pupil as magnification increases.

Exit pupil is therefore an important consideration when comparing objective sizes, but it is not a direct measurement of overall optical quality or image brightness.

Does a Larger Objective Make a Rifle Scope Brighter?

A larger objective can provide a low-light advantage, but a larger objective does not automatically make a scope brighter.

At the same magnification, a larger objective produces a larger exit pupil. That can allow more of the light available from the scope's optical system to enter the shooter's eye when the eye pupil is sufficiently large.

For example:

The 56mm scope produces the largest exit pupil in this example. That does not mean it will necessarily produce a visibly superior image to every 50mm or 40mm scope.

Optical performance depends on the entire system. Glass quality, lens coatings, internal optical design, light transmission, resolution, contrast, and the quality of construction all matter.

This is why comparing scopes solely by objective diameter can produce misleading conclusions. A larger objective provides a larger optical aperture, but it does not eliminate the importance of the rest of the optical system.

Objective Lens Size vs. Magnification

Objective diameter becomes much more meaningful when considered alongside magnification.

Consider a 40mm objective. At 5x, it produces an 8mm exit pupil. At 20x, it produces only a 2mm exit pupil. The objective has not changed, but the amount of light delivered through the exit pupil has changed because magnification has increased.

The same principle applies to larger objectives. A 56mm objective can produce a large exit pupil at moderate magnification, but at very high magnification its exit pupil becomes considerably smaller.

These figures are calculated exit-pupil diameters. They are not measurements of overall image brightness, light transmission, or optical quality.

This relationship explains why large-objective scopes are frequently paired with high magnification. At high magnification, the larger objective helps prevent exit pupil from becoming excessively small.

Common Rifle Scope Objective Sizes

32mm Rifle Scope Objectives

A 32mm objective is useful when compact dimensions and low weight are important. This size is commonly found on scopes intended for moderate magnification and general hunting applications.

The smaller objective can also make it easier to maintain a relatively low mounting position, although actual mounting height depends on the scope and rifle rather than objective diameter alone.

A 32mm objective is generally best viewed as a lightweight, compact configuration rather than a choice intended to maximize exit pupil at high magnification.

40mm Rifle Scope Objectives

A 40mm objective is one of the most versatile choices for a hunting rifle. It provides a useful balance between optical aperture, scope size, weight, and mounting considerations.

For hunters who primarily shoot during daylight and use moderate magnification, a 40mm objective can provide more than enough optical performance without the additional bulk of a larger objective bell.

It is particularly attractive when keeping the rifle light and maneuverable is important.

42mm Rifle Scope Objectives

42mm objectives occupy a similar role to 40mm objectives but provide a slightly larger aperture.

This size is common on versatile hunting scopes because it offers a practical compromise between compact dimensions and the larger exit pupil available from a larger objective.

For many general-purpose hunting rifles, 40mm and 42mm objectives represent a particularly useful middle ground.

44mm Rifle Scope Objectives

44mm objectives are less common than 40mm, 42mm, and 50mm models, but they provide an intermediate option between the common objective sizes.

The additional aperture can be useful when a scope's magnification range and optical design benefit from a somewhat larger objective without moving all the way to a 50mm objective.

50mm Rifle Scope Objectives

50mm objectives are common on scopes with higher magnification ranges and on optics intended for use during lower light.

At a given magnification, a 50mm objective produces a larger exit pupil than a 40mm or 42mm objective. This can become especially useful when magnification is high enough that a smaller objective would produce a relatively small exit pupil.

The tradeoff is increased physical size and, in many cases, additional weight. The larger objective bell may also require more attention to barrel clearance and mounting height.

56mm Rifle Scope Objectives

56mm is a large objective size commonly associated with high-magnification and low-light-oriented rifle scopes.

At the same magnification, a 56mm objective produces a larger exit pupil than a 50mm objective. This can be useful when a shooter needs high magnification while ambient light is decreasing.

The practical advantages come with corresponding compromises. A 56mm scope can be larger and heavier, and the physical dimensions of the objective bell can affect mounting height, barrel clearance, and cheek weld.

40mm vs. 50mm Rifle Scopes

The 40mm-versus-50mm comparison is one of the most useful ways to understand the tradeoff involved in objective diameter.

At 10x, a 40mm objective produces a 4mm exit pupil, while a 50mm objective produces a 5mm exit pupil. At 20x, the difference is 2mm versus 2.5mm.

The 50mm objective therefore provides a measurable advantage in exit pupil at the same magnification. The question is whether that advantage justifies the additional size and weight of the scope for the intended rifle.

For a lightweight hunting rifle used primarily during daylight, a 40mm objective can be the more practical choice. A 50mm objective becomes more compelling when the scope's magnification and expected shooting conditions make the additional exit pupil useful.

50mm vs. 56mm Rifle Scopes

The difference between a 50mm and 56mm objective is smaller than the difference between a 40mm and 50mm objective, but it can still be relevant in specialized applications.

At 10x, a 50mm objective produces a 5mm exit pupil while a 56mm objective produces a 5.6mm exit pupil. At 20x, those figures become 2.5mm and 2.8mm.

The 56mm objective therefore provides additional exit pupil, but the improvement must be considered alongside the physical size and weight of the scope.

For a rifle that spends most of its time in daylight, the additional objective diameter may offer little practical benefit. For a high-magnification optic used in low light, however, the larger objective can be worthwhile.

42mm vs. 50mm Rifle Scopes

A 42mm objective is often a strong choice when portability and a relatively compact scope are important. A 50mm objective shifts the balance toward a larger exit pupil and greater low-light potential.

At 10x, the difference is 4.2mm versus 5mm of exit pupil. At 16x, it becomes approximately 2.6mm versus 3.1mm.

Neither configuration is inherently better. A hunter carrying a lightweight rifle through steep terrain may place more value on the compact 42mm configuration, while a hunter using a higher-magnification scope from a fixed position may prefer the additional aperture of a 50mm objective.

What Objective Size Is Best for Hunting?

There is no universal objective size for hunting. The appropriate choice depends on the rifle, hunting environment, magnification requirements, shooting distance, and expected lighting conditions.

For many general-purpose hunting rifles, a 40mm or 42mm objective provides an excellent balance of performance and portability. These sizes are particularly practical when the rifle will be carried extensively and most shots occur during adequate daylight.

A 50mm objective becomes more attractive when low-light performance or higher magnification is a significant consideration. A 56mm objective can make sense when maximizing exit pupil at high magnification is important enough to justify the additional size and weight.

The best hunting scope is therefore not necessarily the scope with the largest objective. It is the scope whose objective, magnification range, optical system, and physical dimensions match the way the rifle will actually be used.

What Objective Size Is Best for Low-Light Hunting?

For low-light hunting, a larger objective can provide an advantage by maintaining a larger exit pupil at a given magnification.

This becomes especially relevant when the shooter needs to increase magnification as light levels decrease. For example, a 40mm objective at 10x produces a 4mm exit pupil, while a 50mm objective at the same magnification produces 5mm.

However, objective diameter should never be considered in isolation. A high-quality optical system with good glass, coatings, and light transmission can outperform a larger objective that uses an inferior optical design.

It is also important to remember that legal shooting light, target identification, and the ability to distinguish the reticle from the target are practical considerations. Maximum theoretical exit pupil does not guarantee that a scope will provide a usable image under every low-light condition.

What Objective Size Is Best for Long-Range Shooting?

Long-range scopes frequently use 50mm or 56mm objectives because they are often paired with high magnification.

As magnification increases, exit pupil decreases. A larger objective helps preserve a larger exit pupil at those higher magnifications.

For example:

That does not mean a long-range scope must have a 50mm or 56mm objective. If the rifle is used primarily in daylight, a smaller objective may provide an excellent balance of optical performance and reduced weight.

For a long-range rifle that is used in variable lighting, however, the additional exit pupil provided by a larger objective can become increasingly useful.

Does a Larger Objective Require Higher Scope Rings?

Not automatically, but a larger objective can create additional clearance requirements.

Scope ring height is determined by the physical relationship between the scope, rifle, mounting system, and shooter's preferred position. Objective diameter is only one part of that equation.

A larger objective bell may need to clear the rifle barrel, receiver, handguard, or other components. The shape of the objective bell matters as well; two scopes with the same nominal objective diameter can have different outside dimensions.

Ring height should therefore be selected using the actual dimensions of the scope and rifle rather than assuming that every 50mm or 56mm scope requires a particular ring height.

The goal is to achieve sufficient clearance while keeping the scope as low as practical for a comfortable and repeatable shooting position.

Does Objective Size Affect Cheek Weld?

It can, particularly when a large objective requires the scope to be mounted higher.

A higher-mounted scope changes the relationship between the shooter's eye and the rifle stock. On some rifles, this can make the shooter's natural cheek weld less effective and may require an adjustable cheek rest or other stock modification.

This is one reason objective size should be considered as part of the complete rifle configuration rather than as an isolated optical specification.

A lightweight hunting rifle with a traditional stock may benefit from a smaller objective and lower mounting position, while a precision rifle with an adjustable stock may make it easier to accommodate a larger optic.

Does Objective Size Affect Scope Weight?

Larger objective lenses generally contribute to larger and heavier scopes, although objective diameter is only one factor that determines overall weight.

Magnification range, maintube diameter, turret configuration, optical construction, adjustment mechanisms, and other features can have a substantial effect on scope weight as well.

The difference matters most on hunting rifles that are carried for long distances. A larger objective may provide useful optical benefits, but those benefits should be weighed against the weight of the complete rifle, scope, rings, and mounting system.

Does Objective Size Affect Field of View?

Objective diameter does not directly determine field of view.

Field of view is primarily influenced by magnification and the scope's optical design. At a given scope design, increasing magnification generally reduces the amount of terrain visible through the optic.

A larger objective should therefore not be selected because you expect it to provide a wider field of view. A 56mm scope is not inherently wider than a 40mm scope simply because its front lens is larger.

If a wide field of view is important, compare the manufacturer's published field-of-view specifications at the magnifications you are most likely to use.

Does Objective Size Affect the Eyebox?

Objective size can influence the exit pupil available at a particular magnification, but objective diameter does not by itself determine how forgiving a scope's eyebox is.

The eyebox describes the range of eye positions from which the shooter can obtain a complete, usable sight picture. Eyebox performance depends on the scope's overall optical design, including the eyepiece and internal optics.

Two scopes with identical 50mm objectives can therefore have noticeably different eyebox characteristics.

A larger objective can provide a larger exit pupil at the same magnification, but that should not be confused with a guarantee of a more forgiving eyebox.

Objective Size vs. Glass Quality: Which Matters More?

Objective diameter is only one component of optical performance.

A larger objective provides a larger aperture, and it can provide a larger exit pupil at a given magnification. But the quality of the image ultimately depends on the entire optical system.

When comparing rifle scopes, consider:

• Objective diameter
• Magnification range
• Exit pupil
• Glass quality
• Lens coatings
• Light transmission
• Resolution and contrast
• Optical design
• Eye relief
• Eyebox performance
• Scope weight
• Mounting requirements

A high-quality 40mm scope can therefore be a better choice than a lower-quality 50mm scope, depending on the intended application. Conversely, a well-designed 50mm or 56mm scope can provide a meaningful advantage when its larger objective is being used to support high magnification in low light.

How to Choose the Right Rifle Scope Objective Size

The easiest way to choose an objective size is to start with the rifle's intended use rather than the objective diameter itself.

These are starting points, not rules. The appropriate objective size depends on the complete scope configuration and how the rifle will be used.

Consider How Much Magnification You Actually Use

If most shots are taken at 4x to 8x, there may be little reason to choose an exceptionally large objective solely for exit pupil. If you routinely use 12x, 16x, 20x, or higher magnification, objective size becomes increasingly relevant because exit pupil decreases as magnification increases.

Consider When You Hunt

A hunter who primarily hunts during bright daylight has different optical requirements from someone who routinely hunts during the first or last available shooting light.

If low-light performance is a priority, compare objective size, magnification, and the overall optical quality of the scope rather than relying on objective diameter alone.

Consider Rifle Weight

If the rifle is carried long distances, the weight of the scope matters. A larger objective may provide additional optical capability, but that capability comes at the expense of additional bulk in many scope designs.

Consider Mounting Height

Check the actual dimensions of the scope and rifle before selecting rings. A larger objective bell can affect barrel clearance and may influence how high the optic needs to be mounted.

Consider Your Shooting Position

The best optical configuration is one that allows you to establish a consistent and comfortable cheek weld. If a large objective forces the scope significantly higher than a smaller objective would, the resulting change in shooting position should be part of the decision.

Rifle Scope Objective Lens FAQ

Is a 50mm scope better than a 40mm scope?

Not universally. A 50mm objective produces a larger exit pupil than a 40mm objective at the same magnification, which can be beneficial in low light and at higher magnification. A 40mm scope is generally more compact and can be lighter and easier to mount low on the rifle.

Is a 56mm scope better than a 50mm scope?

A 56mm objective produces a larger exit pupil than a 50mm objective at the same magnification. Whether that difference is useful enough to justify the additional size and weight depends on the scope's magnification, the expected lighting conditions, and the rifle's intended use.

What objective size is best for a deer rifle?

For many general-purpose deer rifles, 40mm or 42mm objectives provide an excellent balance of optical performance, weight, and mounting flexibility. A 50mm objective may be preferable when higher magnification or low-light performance is a priority.

Does a bigger objective lens make a scope brighter?

A larger objective can produce a larger exit pupil at the same magnification, which can provide a low-light advantage. It does not, however, guarantee a brighter image. Glass quality, coatings, optical design, and light transmission also affect image brightness and quality.

Does a 50mm scope need higher rings?

Not necessarily. Ring height depends on the actual dimensions of the scope and rifle and the amount of clearance required. A larger objective bell may require additional clearance, but objective diameter alone does not determine the correct ring height.

Is a 40mm scope enough for hunting?

For many hunting applications, yes. A 40mm objective can provide an excellent balance of size, weight, and optical performance, particularly when the rifle is used primarily during daylight and at moderate magnification.

Why do long-range scopes have 50mm or 56mm objectives?

Long-range scopes are frequently used at higher magnification. Because exit pupil decreases as magnification increases, a larger objective can help maintain a larger exit pupil at high magnification.

Does objective size affect field of view?

Objective diameter does not directly determine field of view. Magnification and optical design are much more important factors. Compare published field-of-view specifications if a wide field of view is important to your application.

Does a larger objective make a scope heavier?

Generally, larger objectives contribute to larger and heavier scope designs, but objective diameter is not the only factor. Magnification range, tube diameter, turret configuration, and optical construction can also significantly affect weight.

What is the best objective size for low-light hunting?

A larger objective can be advantageous when hunting in low light, particularly when combined with higher magnification. However, objective diameter should be evaluated together with the scope's optical quality, coatings, light transmission, and magnification range.

What is the best objective size for long-range shooting?

There is no universal answer. A 50mm or 56mm objective can be useful for high-magnification shooting, particularly when light levels are low. A smaller objective may be preferable when weight, compactness, and a low mounting position are higher priorities.

Does a larger objective give a better eyebox?

Not necessarily. A larger objective can provide a larger exit pupil at a given magnification, but eyebox performance is determined by the scope's overall optical design. Objective diameter alone does not determine how forgiving a scope is to eye position.

Choosing the Right Objective Lens for Your Rifle Scope

Choosing a rifle scope objective size is ultimately a matter of balancing optical requirements against the physical characteristics of the rifle.

A 32mm, 40mm, or 42mm objective can be an excellent choice when low weight, compact dimensions, and a low mounting position are priorities. A 50mm objective provides additional exit pupil at the same magnification and can be particularly useful on scopes intended for higher magnification or lower-light hunting. A 56mm objective pushes that capability further, but also increases the physical size of the optic.

The most important relationship to understand is the one between objective diameter and magnification. A larger objective does not automatically make a scope better or brighter. Instead, it gives the optical system more aperture and can produce a larger exit pupil at a given magnification.

From there, consider the factors that matter to the complete rifle: the magnification you actually use, the light in which you hunt, the distance you typically shoot, the weight you are willing to carry, the required mounting height, and the shooting position you want to maintain.

For many hunters, the best scope is not the one with the largest objective. It is the one that provides the optical performance they need without adding unnecessary size, weight, or mounting complications.