How Do Binoculars Work?

We must have seen binoculars multiple times in our lives. In fact, it is such a common instrument that almost everyone knows how to use it. However, very few know how do binoculars work.

The technology behind a pair of binoculars is quite an amazing play of lenses and light. There is a misconception that a pair of binoculars is a portable or miniature version of a telescope.

The mechanism depends on the science of optics. The concept of binoculars was first known by the public in the year 1854 with the invention of Porro prism technique.

Even though, we have been blessed with new technologies like digital capacity, roof prism system, night vision etc.;

the Porro prism technology is preferred by most customers and manufactures of binoculars.

But before we discuss why prism is important to understand the mechanism of binoculars, we need to discuss about lenses first.

Binoculars Use Lenses

It is true that both binoculars and telescope magnify a specific object. However, the major difference is that binoculars are capable of producing a 3-D like image.

Basically, because of the structure and the mechanism used, we are able to see two images from a somewhat different distance and angle.

This is a result of the space there between both of our eyes. Because of this spacing, each of our eye happen to see the image from somewhat different distance and angle.

Both of the images are merged in this kind of device in order to provide us with a depth perception.

This can be observant in images that are viewed from a close proximity. On the other hand, with the incensement of distance, the difference present among the two images will become lesser.

In order to know how do binoculars work, we have to understand that both the lenses present are different from one another. The one through which we see or the lens that is closest to the eye is given the name ?eyepiece’.

The larger one present on the other side responsible for magnifying the object in question is called ?objective’ lens. There are two types of these lenses that are used by most binoculars’ manufacturers.

These two types are concave and convex type of lenses.

Types of Lenses


Let us first look into the convex type of lens. This type of lens will have a thin outside edge with a fatten middle portion. The path of the light happens to first slow down and then bend towards the center when light enters such type of lens.

So, in a way it brings distant light rays into a much-needed focus. As the light bends in dome like manner, convex lens is also known as converging lens.

Now, because of this converging in the middle, things viewed through this lens appear bigger or magnified. Convex lenses are exclusively used to make magnifying glasses because of this reason as well.

Now, the shape of the concave lens is quite different from convex. This type of lens will have thick outer edge with a thin middle portion. Concave lens will be scattering the light outwards.

As this particular lens happens to spread out light in lines when light enters the lens, it has been given the name diverging lenses. As this lens can diverge or shoot out the light rays, it is exclusively used in movie projectors.

Binoculars happen to use two convex lenses for each eye in series, whereas the objective lens’s job is to gather the light and focus it together for the eyepiece.

The eyepiece after receiving the light will magnify it into a sharpen image which the viewer sees with the help of a pair of binoculars. So, how do binoculars work?

How Do Binoculars Work?


The fact that binoculars are fascinating device cannot be denied by anyone who knows how it works.

You see when light rays happen to travel from a distance far away and then it is focused with the help of a convex lens then there is a chance of over-focusing and crossing over resulting into an upside-down image.

So, you must be thinking: Then, why don’t we see an upside-down image when we use a pair of binoculars? And, this is where prisms are important.

Light Refraction

The process of magnification is only possible because of the light. Thus, lenses were created to capture the light to bend it accordingly.

The process of the light striking the lens and then slowing down and bending is collectively known as light refraction.

So, a pair of binoculars happen to use the different lenses to achieve the desired light refraction. With the shape of the lens, the binoculars happen to control the quality and direction of the light.

Focal Path

As mentioned before, the job of the objective lens is to gather light and focus it. So, when the gathered light is focused, the eyepiece captures it to produce the magnified image.

So, the light needs to travel to a focal point in order to be captured by the eyepiece.

The path travelled by the light is known as focal path. The length of the path depends on the size of the binoculars. And longer the path, the better will be the magnification process.


So, in order to achieve a better focal path in a compact devise, prisms were used to bounce around the light and increased the focal path keeping the design of the device compact.

Binoculars are made by fitting two Porro prisms; the hypotenuses of both of them facing each other.

When light enters through the lens it bounces off on the triangular shaped prisms. After which, it reaches the focal point after travelling the increased the focal path.

Thus, as a result, the viewer is receiving a 3-D image with great clarity.

The Whole Picture

So, it can be said that a pair of binoculars starts out with two objective lenses. The objective lenses are nearest to the object in question, and are made larger on purpose to gather a good amount of light rays.

As these light rays enters the objective lenses, they are bounced around as it hits the prism placed inside the binoculars.

The light rays then travel in the focal path to culminated in its focal point on the eyepiece present nearest to the viewer’s eyes.

It is the job of the eyepiece to produce a ?non-upside-down’ image of the object in question magnified and clarified.

Binoculars now come with many different features like night vision, adjustable magnification, multi-coated lenses, waterproofing and such other beneficial features.

But, by having a slight idea on how do binoculars work, you cannot just look at a pair of binoculars as a simple device with simple features anymore.

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