What Is The Objective Lens Diameter Of A Rifle Scope?

We have done many articles on the intricacies of rifle scopes, from eye relief to magnification range and different reticles. After all, the better you know your rifle scope, the better your hunting capabilities will be. In this article, we look at the lens housed in the objective bell – the objective lens. The objective lens is a vital part of the rifle scope as it directly affects the performance of the scope. Therefore, finding a scope with the right objective lens size is pertinent to an overall enjoyable hunting experience. Let’s dive in and discuss the objective lens.

What Is The Objective Lens?

The objective lens of a rifle scope is the forward-facing lens on a rifle scope. Its purpose is to gather as much usable light around the target downrange from the shooter and transmit it back to the ocular lens. Hence, the larger the objective lens, the more light will be gathered by the scope, resulting in a brighter image.

Typical hunting rifle scopes have an objective lens diameter in the range of 30mm to 44mm – providing a good balance between performance, weight, and size.

How Does The Objective Lens Diameter Affect A Scope?

The diameter of the objective lens directly affects the scope’s functionality in various ways. A Larger objective lenses make the scope heavier and can decrease maneuverability. They are especially cumbersome when hunting in difficult terrains such as dense bush and mountains – I would not advise hunting with anything beyond 44mm in objective lens diameters in this type of terrain.

A larger objective diameter lens can also transmit more light to the ocular lens – resulting in a brighter image. This is especially handy when you hunt in low-light conditions such as dawn, dusk, or heavy cloud cover.

The diameter of an objective lens combined with the scope magnification setting determines the size of the exit pupil – the beam of light that reaches your eye. For instance, a 4x magnification setting with a medium objective lens of 40mm has an exit pupil of 10mm when proper eye alignment is practiced. This is about the maximum the human eye can use, and any larger exit pupil than this doesn’t really provide additional benefit.

Objective lens diameter can also affect image quality. Size is not the only factor that influences image quality. The glass quality combined with the lens coatings on the lenses also influences how much light is gathered by the scope and hence, image quality. For instance, a good quality 36mm objective lens with multiple lens coatings and high-quality glass has an improved and brighter image over a 42mm objective lens with poor-quality glass and scratched lens coatings.

Different Sizes Of Objective Lenses For Rifle Scopes

Objective lenses come in varying sizes, each with its specific use case:

• Small objective lens: These lenses are typically 28mm and smaller. They are generally found in low-powered variable optics (LPVO). They are more efficient for close to medium target engagement, such as military and tactical applications. These scopes provide a low-profile mount and are generally more lightweight and compact than larger objective lenses.
• Medium objective lens: This category is defined by objective lenses in the range of 32 mm – 44 mm. It is also the most popular range for hunting rifle scopes as they offer a good balance between size/weight, cost, and light-gathering capabilities. Some low-light scopes even have objective lenses in the 44m-50mm range.
• Large objective lens: Any lens beyond 50mm is seen as a large objective lens. In our post comparing the 40mm vs 50mm scope we learned the pros and cons of a larger scope. These are specialty scopes that require high-magnification settings or exceptional performance in low-light conditions. Common use cases include varmint hunting or long-range precision shooting. Generally, these scopes are cumbersome, expensive, and difficult to mount.

How Does The Objective Lens Size Affect Scope Mounting?

The size objective lens directly influences how the scope should be mounted on the rifle. Here is a list of the main ways objective lens size affects scope mounting.

• Ring Height: As you start going up in objective lens diameter, you’ll require higher mounting rings so that you have enough clearance between the barrel of your rifle and the scope. Failure to provide proper clearance between these two surfaces will result in the objective bell coming in contact with the rifle barrel, affecting the accuracy of the rifle and can possibly lead to damage to the scope.
• Size and Weight: A larger objective lens makes the scope bulkier and heavier – affecting the balance of the rifle and making it feel top-heavy. Heavier scopes make the rifle unwieldy and harder to handle and often require more robust scope mounts to support the added weight. They can often get snagged on vegetation or other obstacles in the field, which is something you genuinely do not want, as it can ruin your entire hunting experience.
• Cheek Weld: When you raise the scope to compensate for a larger objective lens, you also raise the line of sight, potentially making it hard to achieve a consistent and comfortable cheek weld on the stock.

For more on rifle mounting, you can follow our detailed guide on how to mount a scope. If you don’t mount your scope correctly you’re destined to have accuracy problems before you know it!

Pros & Cons Of Using A Larger Objective Lens

When you use a larger objective lens in your rifle scope, it can offer you both advantages and disadvantages – let’s take a look at some of the key pros and cons.

PROS

Here is a list of the main benefits of using a larger objective lens.

• Light Transmission – The larger your objective lens, the more light is gathered, resulting in a brighter and crispier image with notable improvement in detail and resolution.
• Low Light Conditions Ability – As more light is transmitted, it enables you to hunt at conditions not else wise possible with smaller objective lenses. This makes a larger objective diameter lens better for hunting at dusk, dawn, or very low light conditions, such as in the woods.
• Field Of View – At the same magnification setting, a larger objective lens can provide a wider field of view, which is especially advantageous when tracking moving targets or when you need to survey a large area.

CONS

Here is a list of the downsides of using a larger objective lens.

• Cost – Larger objective lenses are more expensive. This is because they require more materials to manufacture and are more tedious to align, as the larger elements require greater precision when aligning to ensure good optical performance. This is why so many people choose to use our lost of the 5 Best LPVO Scopes instead of larger options.
• Heavier – As already mentioned, the larger the objective lens, the heavier the scope is. This affects the balance of the rifle and can be difficult to handle, especially in challenging terrain.
• Sunlight Reflection – This is a problem I have not yet really experienced, but sometimes a larger objective lens reflects more sunlight and can give away a shooter’s position more easily. However, when you have proper lens coatings and sunshades, you can mitigate the occurrence of sunlight reflection.
• Mounting Difficulty – I have experienced this numerous times – a larger scope is just more difficult to mount due to its size and weight. It is more difficult to find the perfect balance between height and comfortable cheek weld on large objective diameter scopes.

Does Objective Lens Size Affect Eye Relief?

No, not directly – eye relief is the distance between the ocular lens and the shooter’s eye. The eye relief of a scope is generally determined by the design of the eyepiece and the internal arrangement of the lenses of the scope.

However, the objective lens size can affect eye relief in terms of cheek weld. When the objective lens is large, the scope needs to be mounted higher to compensate for the increased size of the lenses. This can result in an uncomfortable cheek weld and affect eye relief as the shooter struggles to find a comfortable shooting position.

How Big Is The Objective Lens On Binoculars?

The objective lens size on binoculars is very important for me when hunting as I use binoculars to spot my target. Larger lenses allow you to spot game much faster, but it also means your arms get tired more quickly – something I can endure if it means I get to spot game faster. Here are some common objective lens sizes for binoculars:

• Compact: Sizes less than 30mm (8×25 and 10×28)
• Medium: 30mm – 40mm (10×30, 8×38) – great for hunting in woods or dense shrub
• Large: 30-50mm (10×44, 12×50) – my favorite is the 10×48, which is well-balanced between magnification and light transmission.

How Big Is The Objective Lens On Monoculars?

Monoculars used for hunting generally have objective lens sizes in the range of 20mm to 42mm. Monoculars are essentially a one eyed binocular. I prefer the upper range in terms of size (42mm) as I enjoy sitting on an elevated area and scoping out an area thoroughly – you never know if you might miss a mountain goat camouflaged between some rocks and snow.

Frequently Asked Questions

The Bottom Line

In conclusion, the objective lens size directly affects the performance of your rifle and your shooting capabilities. A larger objective lens enhances your ability to spot targets, especially in low light conditions, as more light is transmitted, resulting in a clearer image. However, a too large objective lens can decrease your shooting performance because the scope can become too heavy and top-heavy. It can also require a higher mounting, which can lead to an uncomfortable shooting position. Therefore, it is important that you find the balance between size and light transmission – a good size to go for is a 42mm objective lens.