Like any devices, one thing that first comes to the mind of a new buyer of a binocular that engraved with his own units of measurement and technical terms is, “What do the numbers that appear in the binoculars mean?“.
Before purchasing binoculars for hunting or bird watching or astronomy, it is important to understand what the numbers on the binoculars mean. Different binocular models have numbers like 10×42 and 15×56, which give you a wide range of information about the device.
In this article, we will look at what the numbers that appear in the binoculars represent, what are the properties to consider, how to choose the right model for you, and the key technical terms used by the manufacturers.
1. What do the magnification numbers on the binoculars indicate?
The magnification number in the binocular is expressed as part of a combination of two factors. That is, those numbers represent the magnification range and size of the objective lens. One of the most common magnification and objective sizes is 10×42. Where 10x is the magnification range and 42 is the size of the objective lens.
When viewed through a binocular, the image of the object appears larger as the magnification limit increases. For example, if you want to use binoculars to detect small things in the distance in dense forests, 15x power is more appropriate than 8x power.
At the same time, if you want to see a wider area called the FOV (field of view), it is best to choose a lower power such as 8x. Although a larger objective lens collects more light it also increases the overall weight of the device. For instance, 10×56 would have better low light capabilities than 10×42, but it would be heavier.
2. Objective Lens Size
The number following the magnification power refers to the objective lens diameter, also known as the aperture. An objective lens size is a significant number because it determines the amount of light gathered and the field of view. The 10×50 binoculars have a 50mm objective lens and the 7×35 binoculars have a 35mm objective lens.
As more light is collected through the wide objective lens, the image of the target will be brighter. This feature is especially important for viewing the night sky in low light conditions such as twilight. The problem, however, is that the total weight of the binoculars increases as the size of the objective lens increases.
Larger Lens Diameter = Greater Brightness & Visible Details = Heavier Binocular
Therefore binoculars with a diameter not exceeding 50mm are highly recommended for outdoor activities such as hunting, traveling, bird watching, and night observation. These are lightweight so they are convenient to carry and easy to handle. For trekking and daytime observations, 20mm diameter binoculars are sufficient.
3. Angle Of View
The Angle Of View (AOV) goes hand in hand with the Field Of View (FOV), as the magnitude of the horizontal views visible when viewed through a binocular is the same.
AOV is expressed in degrees. High AOV refers to a wide area, i.e. anything above 6 degrees can be considered good vision. A number as high as 72 degrees will form the true angle.
This number is achieved by multiplying the viewing angle with the magnification value of the binocular. That is, a 10×50 binocular with a 7.2-degree angle has a precise viewing angle of 72 degrees (7.2 x 10 magnification).
4. Field Of View
Similar to the angle of view, the Field of View (FOV) is not expressed in degrees, but rather in feet (1,000 yards) or meters (1,000 meters). If the binoculars have a high FOV, you can achieve a wider horizontal view through the lens. Keep in mind that the field of view will be smaller as the magnification limit increases.
5. Eye Relief Number
Binocular eye relief number is an important feature for you if you are a person who wears glasses. This number indicates how far your eyes are from the device’s eyelids while enjoying the full view provided by Binocular. If you wear glasses, have at least 15mm of eye relief.
6. Exit Pupil Number
Many people do not have a proper understanding of this number. The pupil number is to hold the binoculars at a distance of 8 inches from your eyes. The two points you see in the center of the eyelids, the light of the lens will reach your eyes so that you can see the image you are focusing on.
The value can be easily calculated by dividing the objective lens diameter by the magnification. For example, a 10×50 sized binocular would have a 5mm exit pupil, while an 8×25 would only have a 3.1mm exit pupil. It is generally recommended to purchase binoculars with an exit pupil greater than 4 mm.
7. Close Focus
The most noteworthy aspect we need to focus on in this article on “what are binocular numbers is” the close focus. This number signifies the minimum distance that the binoculars should focus on. That is, if you focus close to 13 feet, you can focus straight on the object 13 feet away from the binoculars.
What do the numbers in the binoculars mean? I hope you now understand the full meaning of the question. When buying binoculars, these numbers will be the guide to finding the right one for you.
If you want to see the stars at night, choose a binocular with a big aperture. Choose binoculars with small aperture if low weight and portability are important to you.