If you are thinking of buying a pair of binoculars for birding, watching sports, or hunting?
If so, it is important to understand what do the numbers on binoculars mean. These will give you all the information you need to know about the binoculars, which will make sure that you buy the perfect pair for your needs.
So, let’s look at these numbers in more detail…
- 1 What Do the Magnification Numbers on Binoculars Mean?
- 2 What is the Objective Lens Size (Aperture)?
- 3 What is the Angle of View (AoV)?
- 4 What is the Field of View (FoV)?
- 5 What is the Eye Relief?
- 6 What is the Exit Pupil Number?
- 7 What Does the Close Focus Number Mean?
- 8 An Overview
- 9 Looking for More Great Info on Binoculars?
- 10 Final Thoughts
What Do the Magnification Numbers on Binoculars Mean?
The magnification of a pair of binoculars is shown as the number before the ‘x,’ for example, 8×40 or 10×50.
The number, for example, 8x, refers to the power of magnification. In this case, a pair of binoculars that has an 8x magnification will make an object appear to be eight times closer than it actually is. The higher the number, then the closer objects will appear to be through the lens.
However, very high magnifications, such as 12x or more, will make it difficult to maintain a steady image if the binoculars are being handheld. Therefore, the binoculars need to be stabilized on a tripod (if your binoculars has a tripod mount) or a solid object like a fence post or a wall.
It is also possible to buy zoom binoculars that offer an adjustable magnification range. These will be shown as, for example, 8-12x, with a magnification range of 8x to 12x.
What is the Objective Lens Size (Aperture)?
The number after the ‘x’ is the size of the objective lens size, which is also referred to as aperture. This indicates the light gathering ability of the lenses. Therefore, a 7×35 will feature a 35mm objective lens, and a 10×50 binocular will feature an objective lens that is 50mm in size, etc.
The larger the objective lens size, the brighter the image will be because there is more light being transferred through the lens.
However, larger lenses add a lot more weight. Therefore, depending on how you use your binoculars, there is sometimes a payoff between smaller objective lenses, making them lighter and easier to carry over long distances, compared to the additional brightness of a larger lens.
For example, a 10×40 is usually better for the best hunting binoculars than a 10×50. But if you are on the coast seawatching for birds, then a 10×50 would be a great choice.
What is the Angle of View (AoV)?
This is very similar to the field of view (which I will be covering next) and indicates the amount of horizontal view that is visible when looking through a pair of binoculars. They are often confused, being so similar, which is why I have listed them separately.
The Angle of View is always expressed in degrees, and the higher the number, then the wider the view that you will be able to see. Any number that is higher than 5 or 6 degrees is considered a good angle of view.
However, if you see a much higher number, such as 72 degrees, for example, then the manufacturer is probably listing the actual angle of view. This is calculated by multiplying the angle of view by the magnification, e.g., a 10×50 binocular that has a 7.2-degree AoV will have a 72-degree actual angle of view (10 x 7.2).
What is the Field of View (FoV)?
This is not expressed in degrees but as feet per 1,000 yards or meters per 1,000 meters.
As with AoV, a higher number would mean you will have a wider horizontal view through the binoculars. Under normal conditions, a Field of View of between 300 and 375 feet is around what you should be looking for.
Do you need to convert Angle of View to Field of View?
If so, simply multiply the AoV by 52.5; therefore, a 7.2-degree angle of view equals a 378 feet field of view (7.2 x 52.5 = 378)
What is the Eye Relief?
The eye relief of a pair of binoculars is only important if you wear a pair of glasses. It is an indicator of how far away your eyes can be from the eyepiece while still enjoying the full field of view offered by the binoculars.
Many pairs of binoculars have rubber eyepieces that can be folded back to allow for those who wear eyeglasses. If this is important to you, look out for them.
If you do wear glasses, then you should look for an eye relief of at least 15mm.
What is the Exit Pupil Number?
The simplest way to understand the meaning of this number is to hold your binoculars about eight inches away from your eyes. The two dots you can see in the center of the eyepieces is where the light from the lenses hits your eyes and allows you to see the image that you’re focusing on. These dots need to be bigger than your pupils.
The value can be easily calculated by dividing the diameter of the objective lens by the magnification. For example, an 8×25 binocular will have a 3.1mm exit pupil. Whereas a 10×50 binocular will have a larger 5mm exit pupil.
Any Exit Pupil that is 4mm or larger will be fine for most conditions, but bigger is better.
What Does the Close Focus Number Mean?
The last number in my guide to what binocular numbers mean is the close focus. This is the minimum distance that the binoculars need to be able to focus properly. For example, a Close Focus of nine feet will allow you can get perfect focus on an object that is positioned nine feet away from you.
Now that I’ve gone through in detail the meaning of all the numbers on a pair of binoculars, let’s have a quick overview to help you remember the most important points:
- for low light of nighttime viewing, a larger objective lens diameter is an advantage because it will capture all the available light.
- if you wear glasses, look for an eye relief of 15mm or more
- the higher the magnification, then the smaller the field of view
- take note of the close focus if you intend magnifying very close objects such as birds in bushes
Looking for More Great Info on Binoculars?
Then check out my informative guide to How to Repair Binoculars at Home and Binoculars Parts and their Functions.
Or if you’re after a quality scope for hunting, then take a look at our in-depth reviews of the Best Vortex Scopes, the Best Scope for AK-47, the Best Scope for 6.5 Creedmoor, the Best Scout Scopes, the Best Handgun Scopes & Optics, the Best Ruger AR 556 Scope, or the Best Simmons Rifle Scopes you can buy in 2023.
So, we’ve come to the end of my in-depth guide to binocular numbers.
For most uses, a larger aperture is always best because of the improved light gathering ability, but do take the additional weight into account if you are carrying them over longer distances.
In terms of magnification, again, bigger is better, but remember that the higher the magnification, the smaller the field of view, which will make finding smaller objects at a distance harder. However, avoid magnifications higher than 12x unless you are using a tripod and are happy with the very small FoV they give.
So, when it comes to buying your next binoculars, you should now know everything you need to find the perfect pair!