Birding Hub is reader-supported. When you purchase through one of our links we may earn an affiliate commission (at no cost to you).

What Do The Numbers On Binoculars Mean? (Explained)

What Do The Numbers On Binoculars Mean?

Understanding the numbers on binoculars can be a daunting task for many people. In this article, we will explain what the numbers mean and how they affect the performance of binoculars.

Learning what the numbers mean is crucial when purchasing binoculars to ensure that you get the right ones for your needs. By the end of this article, you will have a good understanding of what the numbers on binoculars mean and how to choose the right pair for your next adventure.

Understanding Magnification

Magnification is the first number in the binoculars' specifications and represents the amount by which the image appears closer than it would to the naked eye. For example, a binocular with a magnification of 8x will make an object appear eight times closer than it would to the naked eye.

What Do The Numbers On Binoculars Mean?

Common magnification powers for binoculars range from 6x to 12x, with some specialty binoculars having even higher magnification.

High magnification can be beneficial for certain activities, such as birdwatching or stargazing, where the ability to see fine details is crucial. However, high magnification can also have drawbacks, such as reduced image stability due to even minor hand movements and a narrow field of view, making it more difficult to locate objects.

When viewing sports or tracking animals in action, lower magnification can provide a wider field of vision and steadier pictures. This creates an optimal experience for the user to capture all the details with ease.

It's important to note that higher magnification doesn't always mean better image quality, as the quality of the optics and the stability of the binoculars also play a role in the clarity of the image. Read the following article to exactly know the distance you can see with binoculars.

Lens Diameter And Objective Lens

The second number in the binoculars' specifications represents the objective lens diameter, which is the size of the lens on the front of the binoculars. Objective lens diameter is typically measured in millimeters and can range from 20mm to 50mm or more, depending on the model.

The objective lens is crucial in determining the brightness of the image and plays a significant role in image quality. Larger objective lenses can gather more light, resulting in a brighter image, while smaller objective lenses produce a dimmer image.

Common objective lens sizes include 25mm, 32mm, 42mm, and 50mm. 25mm and 32mm lenses are typically found in compact binoculars, while 42mm and 50mm lenses are found in full-sized binoculars.

Larger objective lenses can produce a brighter image, but they also make the binoculars heavier and bulkier. Additionally, larger objective lenses can produce a shallower depth of field, making it more difficult to keep objects in focus when changing the distance between the user and the object being viewed.

The quality of the objective lens also plays a significant role in image quality. Higher-quality lenses can produce sharper and more detailed images, with less distortion and chromatic aberration. However, high-quality lenses are typically more expensive, making the binoculars themselves more expensive as well.

Exit Pupil

The exit pupil of a pair of binoculars is the determinant that reveals how much light transmits into its viewers' eyes. Finding the exit pupil size is effortless! All you need to do is divide the diameter of your objective lens by its magnification power. For example, 10x42 binoculars will have an exit pupil of 4.2mm (42mm divided by 10).

Common exit pupil sizes range from 2mm to 7mm, with larger exit pupils providing a brighter image in low-light conditions. However, the size of the exit pupil must match the size of the user's pupils for optimal performance. The human eye's pupil can dilate up to about 7mm in low-light conditions, so an exit pupil size larger than 7mm would be unnecessary.

In low-light conditions, such as dawn or dusk, the exit pupil size becomes particularly important, as it determines the amount of light that reaches the user's eyes. When the exit pupil is smaller than your own, you will be looking at a less vibrant image compared to one that has a larger diameter.

What Do The Numbers On Binoculars Mean?

In addition to low-light conditions, the exit pupil size also affects image quality. If the exit pupil is too small, viewers have a sensation of looking through a "tunnel", with dark edges in their peripheral vision. This can lead to fatigue and an overall lack of clarity when viewing objects far away.

On the other hand, an exit pupil that's too large will cause a 'washed-out' appearance from too much light entering the eyes.

It's important to select binoculars with an appropriate exit pupil size for the intended use. For low-light conditions, a larger exit pupil is desirable, while for activities such as birdwatching or sports, a smaller exit pupil may be sufficient.

Read Also: Learn about the best birding binoculars

Field Of View

The field of view is the width of the image visible through the binoculars, typically measured in degrees or feet at a certain distance. A wider field of view allows the user to see a larger area without moving the binoculars, while a narrower field of view makes it more difficult to locate objects and track moving subjects.

The field of view can be calculated using the magnification power and the apparent field of view. The apparent field of view is the width of the image visible through the binoculars, expressed in degrees, and is typically listed in the binoculars' specifications.

The common field of view sizes ranges from 5 to 10 degrees, with wider fields of view being more desirable for certain activities. For example, birdwatchers may prefer a wider field of view to quickly locate and track birds, while hunters may prefer a narrower field of view for greater magnification when focusing on a specific target.

It's important to note that a wider field of view can come at the cost of image quality, as the optics may not be able to maintain sharpness and clarity across the entire field of view. Additionally, binoculars with wider fields of view tend to be more expensive due to the complexity of the optical design.

Ultimately, the importance of the field of view depends on the intended use of the binoculars. Activities that require tracking moving subjects or a broader perspective may benefit from a wider field of view, while those that require greater magnification and detail may prioritize a narrower field of view.


In conclusion, understanding the numbers on binoculars can help you make an informed decision when purchasing a pair that best suits your needs. The magnification power and objective lens diameter determine the image size and brightness, while the exit pupil and field of view affect image quality and the user's ability to locate and track objects.

When selecting binoculars, it's important to consider the intended use and select a pair that balances magnification power, objective lens diameter, exit pupil size, and field of view. By doing so, you can ensure that you have a pair of binoculars that provide optimal performance for your chosen activity.

Scroll to Top