What Do the Numbers on Binoculars Mean?

If you have ever picked up a pair of binoculars in your hands, you must have noticed an array of numbers engraved on the body. These numbers represent the specifications of a binocular, so it is very important to know what do the numbers on binoculars mean if you are planning on buying a pair.

In this article, we will have a look at each of these numbers individually.

What Do the Numbers on Binoculars Mean

Magnification

You can see a pair of numbers like 10x50, 7x35 printed on binocular frames. The first number of the combination is magnification, or more simply put, it is the number that precedes the multiplication sign. A 10x magnification means the target will appear ten times larger than it does to the naked eye.

Different magnification powers serve different purposes. For example, a 7x binocular should be enough to bring you closer to the action when you are attending a sporting event, but hunters out in the forest would prefer 10x zoom binoculars for locating distant prey times closer.

Objective Lens Diameter

The number that follows magnification in the paired combination denotes the size of the objective lenses. So, a 10x50 pair of compact binoculars has a 10x magnification and a 50mm objective lenses diameter. This measurement helps us understand how much amount of light enters the lens. More light conditions yields brighter images.

Best binoculars get bulkier with increasing objective lens size. 42mm ones are the most popular, but if you intend on doing some night sky observations go for higher lens sizes.

Angle of View/Field of View

Binocular users often get confused with the terms angle of view and field of view. Both of these expressions indicate the same thing using different metrics, which is the width of the area you can view through your optics. A greater angle of view will grant you superior vision coverage across a horizontal plane.

The angle of view is expressed in degrees. Sometimes, manufacturers choose to use the actual angle of view which combines magnification and angle of view. For example, an actual angle view of 72 degrees would indicate a binocular with 10x magnification and 7.2 degrees angle of view.

Field of view, aka FoV, is more commonly used. It is expressed in feet/1000 yards or meters/1000 meters, instead of degrees. You can derive field of view from the angle of view using the following formula-

Field of View=Angle of View x 52.5

A field of view falling within the range of 300 feet/1000 yards to 375 feet/1000 yards (bird watching) should be enough for most binocular users.

Eye Relief

Eye relief is the minimum distance you would need to maintain between your eyes and the eyepiece to experience the full field of view. For spectacle wearers, this distance should be 15mm at least.

Exit Pupil Number

Exit pupil number refers to the size of the dots that appear on the eyepiece as we focus on an object. Light enters in your eyes through these spots and constructs the image of the object in your retina.

Exit Pupil Number=Objective Lens Diameter/Magnification

An exit pupil number greater than 4mm is favorable for most conditions.

Close Focus

Close focus is the lowest distance you need to be from an object to properly focus on it with your binocular. A close focus of 10 feet implies you need to be at least 10 feet away from the target to get an ideal focus. 

Conclusion

Hopefully, now you have a clear idea about what do the numbers on binoculars mean.

Take Care!

Leave a Reply