What Do the Numbers Mean On Binoculars?

What Do The Numbers Mean On Binoculars?
Alfred Mendoza

A pair of binoculars is an intricate lens system, and its technical aspects define its features.

But, what do the numbers mean on binoculars? 

This article is a simple guide to a better understanding of the various numbers when choosing binoculars.

These binocular numbers define certain physical features and attributes. 

An example is A7×50 or 20×80. The first number (7x, 20x) pertains to the strength of magnification. 

And the second number (50, 80) is the objective lens diameter measured in millimeters for light gathering. 

Large objectives collect more light, so the binocular increases the lens size, multiplying the light gathered for the lens diameter.


Why are These Magnification Numbers Important?

Magnification is a crucial factor when evaluating which binoculars are best for which type of usage.  

The primary purpose of binoculars is to enable you to see distant objects more clearly by enlarging them like you were viewing them from a lot closer.

A higher magnification provides more details, but more may not always be better. The physics of light, including low light conditions and brighter images, define the practical limits.

Keep it in mind when you choose binoculars.

Binocular Numbers - Some Elements to Consider


Angle of View

The angle of view correlates with the field of view since they apply to the same subject. The AoV you will notice is presented in degrees. A larger figure translates to a wider field.

For the best angle of view, you can consider anything more than 6°. Occasionally, though, it is mistaken with the field of view. 

Like, supposing the AoV figure is exceptionally high, such as 65, it is the FoV. Usually, manufacturers of binoculars make this kind of misrepresentation. 

The chance is they multiplied the AoV with the magnification value in case you notice an exceptionally high degree of AoV.

Whether you’re watching the night sky, bird watching, or observing sporting events, you must keep in mind the actual angle.

Field of View

It is not shown in degrees, whether meters per 1,000 meters or feet per 1,000 yards. 

For instance, if you are 300 feet, the FoV is 300 ft at 1000 yards. 

Having a smaller field of view can make it more difficult to find moving and small moving objects when searching in the distance. A narrow field, likewise, allows in less light so that enlargements will be somewhat darker. 

Hence, if you’re hunting for a white-tailed eagle or rabbit, you’ll need a wide field of view to have a higher probability of finding the image.

Exit Pupil

The exit pupil size is the diameter of the focused light that hits the eye. To visualize the exit pupil, hold the binocular eight to ten inches from your face and see the tiny dots of light in the middle of the eyepieces.

The size of the lenses is what quantifies the diameter of the exit pupil. 

It’s possible to have more magnification, which factors how you see the image and the exit pupil size. 

You can measure it by dividing the binocular’s magnification and the size of the front lenses (1). Thus, an 8 x 50 binocular has an exit pupil of 6.2 millimeters (80 / 8 = 6.2).

exit pupil

Eye Relief

The distance in mm between the left and right eyepiece and your eye provides the complete field of view without clipping. 

Zoom binoculars have adjustable ones that enable you to place them to their optimal relief value. For example, by rotating a collar or rolling down rubber eyecups, you can get maximum relief.

Typically, 15mm will give the best comfort. Wearing glasses is advised when you wear glasses for long eye relief, which is nice if you plan to look at the night sky with your multi-coated binoculars. 

The eye of an eyeglass wearer usually is further from the lens; thus, the user requires a longer eye relief.

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Close Focus

The close focus number of your binoculars refers to the minimum range to focus. For instance, if the close focus of your binocular is 20 feet, then it implies you can have a sharp focus on the image that is 20 feet away from you.

Close focus is essential when you like to observe something near you meticulously and at close range. 

It is advantageous to people that study birds in their natural environment. The ability to define one kind from another can be a minimal branding that cannot be observed with the human eye alone.

close focus

Objective Lens Size

The objective lens size, including the larger objective lens, is found on the other side you use to scan via binocular, also referred to as aperture.    

The size of the objective is a significant number as it shows how much light the larger lenses can get. The higher the diameter of the lenses, the more light it catches, resulting in a brighter and more excellent resolution. 

Accordingly, the wider the piece, the heavier the binocular, so 50mm is the standard maximum size for hand-held binoculars.

Roof prism binoculars, the prism tends to overlap closely, so it allows larger objective lenses to line up with the eyepiece. Meanwhile, the Porro prism offsets your piece. Keep other factors in mind.


The best magnification power for binoculars is the one that fits your conditions and gives satisfaction in the best plausible manner. 

The 8×25 and 8×42 pair of binoculars have the same magnification, which gives more detail. However, the best binoculars do not have too much magnification.

A pair of 20×50 binoculars will magnify 20 times larger than what you would see with your naked eye. 

These binoculars will give an exit of 2.5mm. Therefore, they are not suitable for a close-range application.  

The optical apparatus has a close-focusing range of 45 feet. Hence, objects that are less than 45 feet will look blurry.

What Binocular Numbers Really Mean

So, this was all about the numbers indicated on your binoculars mean. It’s the most significant number for the objective lenses.

Knowing the numbers on binoculars is the first step in understanding its technical aspects. The first figure is the magnification of higher power, and the second figure is the diameter of the objective lenses.

Keep in mind that there’s an eye relief number of users who wear glasses while using the binoculars at the same time for comfort. 

You also have to note the light-gathering ability and the multiple coatings as fully multi-coated binoculars last longer.


  1. https://www.oreilly.com/library/view/astronomy-hacks/0596100604/ch01s08.html

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