How To Read Binocular Numbers

How To Read Binocular Numbers

Are you into wildlife viewing, hunting, hiking, camping, or any other outdoor activity?

If you are, you may be interested in getting a pair of binoculars. 

Binoculars are optical instruments that allow you to see faraway objects up close.

You can use them for a variety of activities outdoors, or even indoors at the opera!

However, once you start shopping, you will soon encounter various numbers that you won’t be familiar with.

Furthermore, you will need to know how to calculate a few numbers to learn more about the binocular’s features. 

If you are unfamiliar with how this instrument works, these binocular numbers can be quite confusing.

In order to pick a good pair, you will need to know what the numbers represent. 

This guide will tell you everything you need to know about reading binocular numbers.

We will cover magnification numbers, objective lens size, angle of view and field of view. 

Furthermore, you will learn about the eye relief number, the exit pupil number and close focus. 

While these numbers may seem confusing at first glance, you will be a pro by the end of this guide. Let’s get started. 

Magnification Numbers

Magnification Numbers

The first set of binocular numbers we will look at in this guide is the magnification number.

Each pair of binoculars comes with a set of numbers, such as 10×50 or 8×40.

The first number of this set, the “10” and the “8” in the example numbers, is the magnification number. 

The magnification number represents the magnification power of the set of binoculars.

For instance, if the magnification number is “10”, The binoculars would magnify the object in the lens ten times.

Essentially, the first number tells you how strong your pair of binoculars are, which is helpful information when you are shopping for a pair. 

Standard binoculars will come in a range of different magnification powers.

You will typically see binoculars that come with magnification powers of 7x to 12x.

However, there are some specialized binoculars out there that support higher powers of over 15x. 

Objective Lens Size

Objective Lens Size

The objective lens size is one of the most important binocular numbers you will need to pay attention to.

You can find this number in the number pair that lists the magnification power (10×50).

The second number tells you what the objective lens size is of your binoculars. 

For example, if a pair of binoculars is 10×50, then the diameter of the objective lenses is 50 millimetres.

The objective lenses are the lenses that are furthest from your eye and closest to what you are viewing. 

The objective lens size tells you a few things. First of all, it tells you how big the binoculars will be and how heavy they are.

So if you want a lighter pair, try to look for a pair of binoculars with a lower objective lens size number such as 30 mm.

Second of all, this number also tells you how much light they can gather. The bigger the objective lens, the more light the binoculars can collect.

More light is always a good thing. The more light that enters the lens, the more data the instrument can collect.

Binoculars need a lot of data to produce crisp images. 

Angle of View

Angle of View

Angle of view can be a confusing term for some people since this term is often interchangeable with field of view.

While they may refer to similar things, they do not exactly mean the same thing. We will explain what angle of view is in this section.

Angle of view refers to how much of the scenery you can see through your binoculars or the amount of visible landscape.

While this may sound similar to field of view, it is the way you measure it that is different. 

In more technical terms, angle of view refers to the angular extent of the area you can see through the lenses. Angle of view is measured diagonally. 

The main difference between angle of view and field of view is that the angle of view is always represented as degrees and not feet. 

For example, say one of the binocular numbers reads 65 degrees. This number most likely refers to the angle of view since it is expressed in degrees.

Depending on the binoculars’ magnification number, the binoculars will have a 6.5 angle of view.

The way you get “65” is by multiplying the angle of view by the magnification power (which would be 10 in this example). 

Field of View

Field Of View

When it comes to binocular numbers, it is important to understand the field of view since it can affect the kind of image you see through your instrument. 

Similar to the angle of view, the field of view refers to how wide an area you can see through your binoculars.

However, unlike angle of view, the field of view is expressed using units of length like feet or meters. 

Typically, this number is expressed in meters per 1000 meters or feet per 1000 yards. The higher the number, the more square footage you can see. 

Something to keep in mind about the field of view is that having a narrower field of view will mean that your instrument won’t take in as much light.

Less light may lead to a lower-quality image in low-light environments. 

Furthermore, a wider field of view will make it much easier to spot small animals in the distance.

If you will use your binoculars for mostly wildlife watching or hunting, having a wide field of view is a good idea. 

Eye Relief Number

Eye Relief Number

The eye relief number is one of the binocular numbers that only some users need to pay attention to. If you wear glasses, then this number will be important. 

The distance between the eyepiece and your eye is called the eye relief.

The exact measurement is the distance that you can see the whole field of view through the binoculars.

If you wear glasses, it is best to use a pair of binoculars with long eye relief.

A longer eye relief will give you enough room to look comfortably through the instrument while wearing your glasses.

Additionally, you can still see the full image without experience any vignetting if you have a long eye relief. 

Exit Pupil Number

Exit Pupil Number

Another one of the most important binocular numbers, the exit pupil, is related to how bright the image will be. 

You can find this number by dividing the objective lens diameter by the binocular magnification number.

For instance, if you have a pair of 8×32, you would divide 32 by 8 to get 4. So your exit pupil would be 4mm. 

The general rule of thumb for exit pupil numbers is the higher the number, the brighter the image will be. 

If you plan to use your binoculars in low-light situations such as evening wildlife watching, you will want a higher exit pupil.

High numbers will indicate better low-light viewing since more light will travel into the lens.

More light in the lens will help produce better images with greater detail. 

Try to get an exit pupil that is 5mm if you are going to use your binoculars in low-light settings such as dusk, dawn, or in the shade.

However, if you mostly use your binoculars during the day when there is lots of light available, exit pupils around 2mm will be adequate. 

Close Focus 

Close Focus 

Last but not least, close focus is another set of binocular numbers that is important to understand. 

Close focus refers to the minimal distance that the binoculars can focus.

For instance, if your pair of binoculars have a close focus of 15 feet, then your binoculars will be able to focus on an object that is 15 feet or more away. 

However, with a close focus of 15 feet, you can’t focus on an object closer than 15 feet. The object will be blurry. 

If you are interested in doing some close-up wildlife watching, such as bird watching or studying insects like butterflies, make sure you have a low close-focus number.

An ideal close focus number for these activities will be around 10 feet or less. A standard pair of binoculars will come with a close focus of around 20-25 feet. 

Conclusion

We hope that this guide has helped you learn how to read binocular numbers. 

The main binocular numbers are the magnification numbers, objective lens size, angle of view, field of view, eye relief number, exit pupil number and close focus. 

When shopping for a new pair of binoculars, the first pair of numbers you will see is the magnification and objective lens size numbers. 

Let’s say you are looking at a pair of 10×50 binoculars.

The first number represents the magnification power (a 10×50 pair magnifies your image ten times), while the second number refers to the size of the objective lens in millimeters (50mm). 

Both the angle of view and field of view refers to how wide of an area you can see through your lens.

The main difference is that the angle of view is measured in degrees while the field of view is expressed using units of length. 

Before you buy a pair of binoculars, make sure to review all of the numbers on the instrument.

These features can greatly affect your viewing experience, and some numbers will be better for certain activities than other numbers. 

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