What Do Binocular Numbers Mean? – Simple Explanation

If you’re an outdoor person, then you probably own a pair of binoculars. Binoculars are decent optical devices that bring clarity to your outdoor experience.

From hunting, boating to birding, binoculars come in handy helping you see things pretty close. Just like any optical device, binoculars have their own measurements.

Ever known the meaning of the numbers on the binoculars? If yes, then you’re an expert outdoorsman. But if you don’t, then you’re at the right place to learn.

Join me as I discuss the meaning of the numbers on a binocular and how to choose a binocular that best suits your needs.

What Do Binocular Numbers Mean?

The numbers on a binocular simply stand for the magnification and the size of the objective lens.

Magnification number and objective size number are shown by two numbers separated by an X. 

Let’s have an example of the most common magnification and objective lens size. 10X42 which is usually 10-by-42.

The 10 in the example above is the magnification and read as 10X. It shows you’ll see the image size 10 times. The second number is the objective lens size and is usually shown in millimeters.

A magnification number tells you how many times the image will appear bigger. A 12x by 50mm binocular will magnify the image 12 times. The objective lens on this case is 50mm.

50mm is the diameter of the objective lens. The diameter of the objective lens is what gathers the light that illuminates the image. A larger objective lens means more light passing through and more clear images. However, it also means a bigger and bulkier binocular.

For instance, a 10×52 binocular reading will have more light in lowlight conditions than a 10×42 binocular. But a 10×52 binocular will be bulkier and larger.

Let’s break this down in detail by looking at the magnification and objective lens size in detail.

Magnification in a binocular

As indicated earlier, magnification is the first number on the binocular. It’s a number that indicates the number of times the image will appear close.

The higher the number, the bigger the magnification. Greater magnifications however mean a lower angle of view.

Are you seeing a bigger image in the eyes? Then it means the angle of view is narrow. This is the framing space.

When using binoculars, hand vibrations can make the framed space unclear. The situation can become worse with a larger magnification.

Generally, binoculars with 10X magnification or more require a tripod stand to ensure better clarity and detailed observations.

Choose a lower magnification when you’re not after fewer details on the frame. A bigger magnification is only needed when you want fine details.

Lens Diameter

The lens diameter is the second number after the X. It is the diameter of the objective lens. The diameter is expressed in millimeters and determines the amount of light passing through to the lens.

Additionally, the lens diameter affects the size of the field of view.  Lens diameter is an important feature to consider when buying a new binocular.

If you’re planning to use the binoculars at sunset and sunrise, then consider one that allows more light to pass to the lens.

Generally, a larger lens diameter equals more brightness and visible lights. However, it also means more weight.

Larger lenses simply means the binoculars will be heavier. Weight is a great consideration for birding, travel and other outdoor activities.

The ideal weight binoculars should be those with 50mm lens diameter or less. Such binoculars are pretty lightweight and extremely easy to carry.

If you’re observing at night, or when light conditions are low, then a 50mm lens diameter is okay. But for daylight trekking, a lens diameter of 20mm works just fine.

Difference between a 10X42mm and a 12X52mm binocular

To have a better understanding of the meaning of the numbers on a binocular, let’s dig deep and see the two examples.

A 10X42mm binocular is one with a 10X magnification and an objective lens of 42mm. The second binocular has a magnification of 12X and an objective lens of 52mm.

 The first binocular will show images 10 times larger while the second will show images 12 times larger.

On the objective size, the first binocular with 42mm will collect less light than the 5mm objective lens. The second binocular will also have a wider field of view.

But we need a tripod case in the 12X52mm binocular to have a better view.

Are those the only features to consider? Knowing what the numbers on a binocular mean is important. But you also need to learn a few crucial features before making any purchase.

Other factors to consider when choosing a binocular

Apart from the numbers on the binoculars which show the magnification and objective lens, there are a few things to consider when choosing a new binocular. These factors include:

Field of View

This is the area one observes through the binocular at 1000m. It’s expressed in degrees and meters.

A small magnification will have a bigger field of view than a larger magnification.

Output Pupil

Exit pupil is expressed in millimeters and makes another consideration. Exit pupil is basically the lens diameter divided by the magnification.

For example, a 12X50mm binocular will have an exit pupil of 4.5.

A 4.5mm exit pupil reading is the best guaranteeing excellent daytime and low light binocular views.

Eye relief

This is the distance between the eyes and the lens. In most binoculars, eye relief varies from  5mm to 20mm.

This is a great consideration for persons that wear glasses. You want to be sure you’re buying a binocular model that will fit.

Generally, greater eye relief means you will have a better view even with glasses.

Types of lenses

Lastly, you need to consider the types of lenses on the binocular.

Plastic lenses are among the best despite a decline in the quality of the images. They result in relatively cheap binoculars and can withstand falls and impacts.

We also have glass lenses which are of good quality allowing light to pass through. They produce quality images but result in higher binocular prices.

Other types of lenses include coated, multi-coated, fully-coated, multi-fully coated and multi-layer FC and MFC.

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