Binocular Numbers & Terminology Explained

(Last Updated On: January 17, 2021)

Considering that binoculars are built to add clarity to your outdoor experiences while trying to determine which pair of binoculars is right for you, it is amazing how complicated things get. Going to a store and browsing through many before you make a final choice is the best way to test the optical performance and ease of use for a pair of binoculars. They represent all binoculars using a couple of numbers, such as 7-50 or 8-30. The first number, including x define magnification or ‘power.’ This shows the degree to which the observed object is expanded. A 7x binocular, for example, makes an item appear seven times nearer than when seen by the naked eye.

There are several models of binoculars that provide variable magnification, typically in the range of 5x to 8x. Because of the low optical efficiency and fragile mechanics, they are called zoom binoculars and are not very good for astronomical observations in most cases. The best thing to do is to avoid them and stick with the ordinary binoculars with fixed strength.

Size of Magnification & Lens

Usually, you’ll see binoculars named 10×50 or 20×60, but what does that number mean?

The magnification is the first number. We looked through a pair of 10×50 objects, 20x60s double that magnification will appear ten times closer than with the naked eye. Different applications need varying degrees of an exaggeration, and they suggest the best ranges on the buying advice page.

The variable zoom is defined as 10-30×50 and can be magnified by any amount from 10 to 30 times. These have a small lever to control magnification near your right thumb.

The size of the objective lens in mm is the second number. The oversized lenses at the far end of the binocular are the goals.

Big targets absorb more light, quadrupling the light obtained by doubling the diameter of the lens. This is especially important in low light conditions, such as bird watching at dusk or astronomy. But while 100mm targets provide outstanding accuracy, they make for a large pair of binoculars that are tiresome and cumbersome to carry. We are finding a perfect solution for the way you use your binoculars, as in all things.

The View Field

Quite literally, the smaller the region you can see at once, the greater the magnification. This is expressed either in degrees or the number of meters observable at a range of 1000m, for example, 4.3 degrees or 114m/1000. You’ll want a large field of view to have a better chance of finding it when you’re hunting for the elusive deer or sea eagle. You’ll need to pan it around binoculars more with a small field of view and can miss the wildlife you’re looking for. So we need the right combination of magnification and field of view.

Pupil Exit Size

That is another significant factor in deciding in low light conditions how well binoculars perform. The diameter of the actual beams of light exiting the eyepieces is the exit pupil dimension.

The magnification is determined by dividing the diameter of the objective lens. But there will be an exit pupil scale of 60/10 = 6mm for 10×60 binoculars.

Relief for the Eye (And Spectacle Wearers)

Eye relief is the amount you can get from the eyepiece in mm to see the whole field of view your binoculars have. This is a challenge for spectacle wearers as their eyes would be further back. You know the middle of the picture when you use binoculars with an eye relief of less than 10mm! A bit like masking off your TV set’s outer section.

The majority of binoculars would have 8-13mm eye relief. But our LE models have a figure of about 18 mm, so anyone who wears glasses will make all the difference. LE versions of the most famous models are offered.

The Forms of Prism

  • Two forms of prisms, BAK-4 and BAK-7, are widely used.
  • BAK-7 prisms are cheaper and are made of less thick glass
  • . The prisms of BAK-4 are denser, dearer, and express more light.


This is where the real difference is found between poorly made binoculars (not always a low cost!) and professional binoculars. It’s a subject on which there is a lot of misinformation and misunderstanding as well. We’re going to try and clearly and accurately describe it.

To increase the quantity of light they absorb, binocular lenses have optical coatings. The coating decreases the amount of light that is reflected and lost away. Early binoculars conveyed just 50 percent of the light they collected! Our layers are unbelievably thin and must be applied to a very high degree of precision with equal thickness. This isn’t a cheap method; too many brands are cutting corners!



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