How Do Binoculars Work?

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Binoculars cleverly use the concept of optics to enable us to view distant objects with ease. Their design is based on the principles of light refraction.

As a kid, I always wanted to own a super-cool pair of binoculars that the S.H.I.E.L.D. agents used in Marvel movies. Imagine being able to look through walls and see every technical detail of your surroundings.

Binoculars may not be superhero-level tools, but they cleverly use the science of optics to zoom you inside an anthill or out to the middle of the Milky Way. In this article, we will learn how exactly this cool gadget works, so that the next time you come across a pair, you’ll know what’s really happening!

Binoculars are essentially a pair of telescopes mounted on a single frame. Though telescopes trace their history back to the 15th century, J.P. Lemeire is credited with the design and patent of the binoculars, which were developed in 1825. Fast forward to 1854, when Ignazio Porro came up with the concept of prism binoculars, which laid the foundation for the incredible technological advancements of binoculars.

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Optics Behind The Binoculars

Binoculars work on the concept of light refraction, and the “magic” element is how lenses/prisms effectively implement this property of light.


When light passes through different media, it bends outwards or inwards, depending on the density of the medium through which it’s traveling. This is called the refraction of light. If light travels to a denser medium, it bends inwards, whereas if it travels to a rarer medium, it bends outward.

diagram to show the refraction of light rays pass through different media
The diagram shows the mechanism of light refraction through different media (Photo Credit : Amalakanti Satya Sarada/Shutterstock)

The glass in the objective lens of the binoculars receives the incident light, and when light passes through them it bends or refracts to form an image. Therefore, the amount of light can be controlled by altering the objective lens. The glass in the eyepiece further receives light through the objective lens and processes its image into the final image perceived by the observer.

Lenses And Magnification

The word lens comes from the Latin word for lentil, in reference to its shape. Therefore, a lens is a piece of curved glass through which light can be transmitted or refracted.

Primarily, there are two types of lenses—convex and concave.

Convex and concave lens, vector illustration diagrams. Labeled scheme with light ray direction and bending through lens. Controlling focal length and focus point for optometry equipment
A convex lens is also known as a converging lens, whereas concave lens is known as a diverging lens (Photo Credit : VectorMine/Shutterstock)

The convex lens is thicker in the middle and thinner towards the sides. This construction helps light refract inwards and allows for focusing distant rays into a smaller region, forming a small image of the distant object. It is used as the objective lens of the binoculars.

The concave lens, on the other hand, is thinner in the middle and thicker towards the side. The light refracts outwards, forming comparatively larger images of smaller objects. Hence, it behaves like a magnifying glass. The eyepiece of binoculars is made of this type of lens so we can clearly see the image of the object.

Prisms And Their Arrangement

The whole construction of binoculars is now coming together, but there’s a catch. It just so happens that when light from a very faraway object passes through the convex objective lens, it produces an upside-down image, resulting from the crossing over of light. The eyepiece also cannot resolve this problem, so the final upside-down image won’t be of any use. This is where prisms come to the rescue!

A prism is a three-dimensional piece of glass that can rotate and reflect an image. Thus, prisms are deployed in binoculars to rotate the inverted image by 180⁰ and obtain an upright image in the eyepiece. Each prism can rotate light by an angle of 90⁰.

A set of two prisms in each tube is used to obtain the desired image in a pair of binoculars. There are two types of arrangements for the prisms, namely Porro prisms and Roof prisms.

Porro and roof prism design of binoculars
Binoculars are based on two types of prism arrangements- Porro Prisms and Roof Prisms (Photo Credit : Dn Br/Shutterstock)

In Porro prisms, the two prisms are arranged side by side at 90⁰. This results in a bulkier structure to the binoculars.

In Roof prisms, the two prisms are arranged in a straight line along the direction of light propagation, which results in more compact binoculars.

Also Read: How Do Different Types Of Telescopes Work?

How Do Binoculars Work?

Putting all the above inferences together, we conclude that when rays of light passing through the objective lens form an inverted image of the distant object, the arrangement of the prisms rotates it by 180⁰ and the eyepiece, in turn, produces a magnified image of the initial image, enabling the observer to easily view that object with clarity. This happens for both the left and right tubes of the binoculars.

Different Types Of Binoculars

With advancements in science and technology, devices are becoming better each day. Binoculars have broadened their horizon of versatile use and are now classified into some specialty categories listed below:

Mini Binoculars

These are portable and can be stuffed into your backpack quite easily. They may be not as powerful as the full-sized ones, but still serve the purpose of magnification quite well.

Mini Binoculars are most widely and generally used (Photo Credit : Grey Carnation/Shutterstock)

Zoom Binoculars

These types of binoculars specialize in changing the magnification of the lenses according to your requirements and are able to zoom in on objects.

Zoom Binoculars are often used to spot wildlife (Photo Credit : HTWE/Shutterstock)

Wide-Angle Binoculars

As the name suggests, these binoculars have a wider field of view than normal binoculars, enabling you to cover a better range to spot objects in open spaces. These are ideal for wildlife and game spotting.

Wide-angle Binoculars are used to keep watch over wide stretches of terrain (Photo Credit : Eva Alex/Shutterstock)

High-powered Binoculars

These are used as an alternative to telescopes by astronomers. They are ideal for long-distance viewing, due to their high level of magnification.

High-powered Binoculars are best-in-class and commonly used for sky-gazing (Photo Credit : Levranii/Shutterstock)

Night-vision Binoculars

These are probably the coolest type of binoculars, as they can enable you to see distant objects in the dark. Used especially by the military or special forces, these binoculars make use of photo-sensitive lenses and photo-cathodes. Thermal imaging may also be available in these binoculars.

The coolest of all, Night-vision Binoculars are widely used by military forces all over the world (Photo Credit : Giorgio Rossi/Shutterstock)

Also Read: Which Is Better: Optical Microscope Or Electron Microscope?

A Final Word

Whether a secret agent, a celebrated soldier, or a wildlife enthusiast, when on a mission or adventure, binoculars are as essential tool. The ability to see what you want beyond the physical limitations of the human eye is quite fascinating.

Do Binoculars make things appear bigger meme
A question to mull over!

Let’s just hope that someday, we can have a device that fits into our eye lens and automatically turns it into a binocular. That ability may not be far away, as technology is evolving fast!

Also Read: Want Eagle Vision? Here Are Some Traits You’d Need.

References (click to expand)
  1. How do binoculars work? - Socratic. Socratic
  2. What Do Numbers on Binoculars Mean? - A Detailed Guide [Upd. 2022] -
  3. How to Use Binoculars (the right way) - Deschutes Land Trust. The Deschutes Land Trust
  4. Binoculars - New World Encyclopedia.
About the Author

Shreya Chakraborty is pursuing her master’s degree in Physics from NSUT, New Delhi. She is passionate about literature and writing, which allows her to express her scientific interests easily and effectively. She enjoys watching Sci-Fi movies, writing poems and articles, and wondering at the beauty of the night sky.

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