How do binoculars work

How do binoculars work

Binoculars are an amazing and fascinating invention. Imagine conveniently viewing the beautiful stars and moon up close in the night sky or a fascinating bird or animal or other distant objects that you cannot get close to physically.

If you own a pair of binoculars, you most probably have a curious mind, and by extension, you might have also wondered at some point how do binoculars work. If yes, then here is your chance to find out.

Understanding how do binoculars work

To put it simply, binoculars are like two telescopes mounted together side-by-side. Here is how the different components work together.


Binoculars and telescopes have special glass lenses that are made of multiple lens elements, which enable control over the bending light rays. Binoculars have two kinds of lenses.

Objective lens: These are convex lenses and are closer to the object in view. The objective lens captures light from the object and causes the light rays to bend through refraction. These converging lens then causes the light to merge when it passes through the glass and focuses it on a point.

Eyepiece lens: The eyepiece lens is like a magnifying glass and magnifies the focused light and brings it to the viewer’s eyes.


The more the magnification, the closer the object will appear. However, higher magnification is associated with less stability and a limited field of view.

Inverted image and image correction

The noteworthy point is that it becomes inverted before the image reaches your eyes. It is because the convex lens or the objective lens causes the light to cross over when it converges.

If you are looking at the stars, an image orientation does not matter. However, for other purposes, it may be a problem. The problem can be fixed through erecting prisms or through a concave lens. The concave lens acts as a diverging lens, stopping the light path from crossing over and preventing the upside-down image. However, higher magnification is a challenge.

Porro Prisms for image correction

Modern binoculars are equipped with erecting prisms that reflect the light. Thus the prisms rotate the image and rectify the image orientation.

The Porro prism binoculars were the first of their kind. The single Porro prism works like a mirror and reflects the light in the same direction but not the same path, rather a parallel path. So, the Porro prism binoculars have two Porro prisms present at a right angle to each other.

It is the placement of the Porro prisms in the binoculars that gives them the particular shape, whereby the eyepiece lens are closer to each other compared to the objective lens.

Roof prisms

In addition to the Porro prism binoculars, the other popular form of binoculars is Roof prism binoculars with the Abbe Koenig or the Schmidt-Pechan prisms.

Prisms make for compact binoculars. It is because the distance between the eyepiece lens and the objective lenses is reduced. They are hence shorter than the refracting telescopes.

We hope you found the article helpful in understanding how binoculars work. Whether you own a basic pair of binoculars or an advanced version like the night vision binocular, a better understanding of their mechanism makes using them even more interesting.