Rangerexpert is audience-supported. When you buy through links on this site, we may earn an affiliate commission that we use for site maintenance. Learn more


How Do Binoculars Work? | Binoculars Parts & Their Functions

how do binoculars work
Written by Marc Niad
Last Update: August 11, 2023

Binoculars are instruments that aid our sense of vision to visualize an object, event, or things that are located far away from us. The device has a corny way of manipulating light. Today we will be looking at its modus of Operandi; i.e., how do binoculars work.

If you intend to gain the full experience of an object that is far away like the moon, stars, or spots favorite birds flying, viewing with the aid of binoculars will be a viable option.

The lenses are designed to bring the action before your vision, regardless of their current distance. The device helps to prevent eye and muscular strain.

How binoculars work Binoculars work by using lenses and prisms to magnify and focus light from distant objects that allows you to see them up close. The objective lenses capture light and form an image, which is then corrected and magnified by prisms and eyepiece lenses. A focusing mechanism helps adjust the image sharpness, and the interpupillary distance adjustment ensures a merged view for both eyes.

How Do Binoculars Work (With Pictures)

Anatomy of a Pair of Binoculars

Let’s get this straight; a telescope is way different from a binocular pair. Although both telescopes and binoculars are known to produce images, in the case of a telescope, the image is not three-dimensional compared to the image formed by binoculars.

Binoculars are used to view images from two different standpoints. This viewpoint is generated because of the space that exists in the eyes, as one eye is meant to view from a different angle and the other eye from another angle.

Both images are then merged together to produce a depth of field. Though the effect of this is seen in objects that are closer. Once there is an increase in distance, the lesser the difference between both images that are formed by the lenses.

The object next to the eye is known as the eyepiece, while the other lenses are called the objective lens, which is very close to the glass that causes magnification. The objective lens and the eyepiece are the essential elements present in all types of binoculars.

Typical porro prism binocular Design

Binoculars have two categories of lenses – the concave and the convex lens

  • Concave lens: this lens is designed to have a bigger out edge and a little middle. It is also known as diverging lenses due to its effect of scattering light.
  • Convex lens: the convex lens is designed to have a little outer edge with a fat middle. Whenever light travels through the lens, its rays tend to be bent in the middle of the lens.

This type of lens is also called a converging lens. Light rays are known to get converged at the center. Objects get magnified if viewed under the lens.

All the forms of binoculars are designed with convex lenses on each side of the eyepiece. This lens is known to interpret the light gathered and focused on it by the objective lens. Afterward, the eyepiece converts the light to a suitable shape that can be interpreted by the eyes.

The Challenges

Whenever a light ray traveling from a distant object is focused on with a convex lens, it can often crossover with each other due to excessive focusing. This can also literally invert an image that is formed on the lens. So, the best way to prevent this occurrence will be with the use of prisms.

The Prism

A prism is a solid glass that carries out the function of a mirror in the binoculars; the only difference it has from a mirror is the absence of a reflective background.

Whenever a prism comes in contact with a ray of light, at an angle that appears to be greater, the ray is simply reflected back with the principle of mirror internal reflection.

Contemporary binoculars are designed to operate with dual prisms that slide out images to 180 degrees, and also help prevent the images from being inverted when it approaches the eyes.

A Quick Recap

The basic function of the objective lens is to gather light from any object it is focused on and make it the central focus. On the other hand, prisms are known to correct every form of image orientation (the image that is inverted) that is generated from the objective binocular lens.

A prism is an element known for correction. It is located between the eyepiece and the objective lens that can invert images to 180 degrees position.

Binocular Styles

To get a perfect idea that governs how binoculars work, you have to know that they are designed in two styles:

  • Roof prism style
  • Porro prism style

The overall weight of binoculars is determined by the kind of prisms it has.

Roof prism & Porro system of binocular

The roof prism is basically used in light and compact binoculars. These types of binoculars tend to be more active once it encounters lesser light that comes into the eyepiece lens.

A roof prism tends to divide the beam or light ray into two and converge the ray or beam again. The entire process leads to phase shifting. Once the ocular is closer, the image inside the roof prism becomes steady. It has a back-to-back kind of arrangement that the roof prism binoculars have.

Porro prism is a type of binoculars that is larger than the roof prism if compared. These binoculars create images that are steady due to the large hinge that exists between both oculars, which gives a more significant range for the adjustments of both lenses.

Although some are of the opinion that the binoculars that porro prism are designed with have a lesser lens power and some form of distance issues between both lenses. But the good news is- irrespective of the odds, the arrangement still works perfectly.

The objective lens of a Porro prism is lined up alongside the eyepiece, right-angled opposite each other. Due to this arrangement, they tend to reverse and erect the image that is produced with the folding light path, which is gathered with the collective lens.

When all the images are organized at 90 degrees angle, it is known as a Porro prism. In such a scenario, one of the prisms tends to change the picture direction to 90 degrees by merely flicking it to one end while the other prism tends to rotate at 90 degrees. Both prisms tend to invert the images that are formed on them.

Magnification Numbers of Binoculars

When learning about how binoculars function, you will notice a specific number known as magnification number. This number shows the amount of light that is gathered by the lens of the binoculars.

8 x42 is an example of a magnification number. The second number embedded in the binoculars is known as the diameter of the objective, while the magnification of the binoculars is represented by the number that comes first. All numbers are embedded on the surface of the pair.

The magnification explains the way an object appears before the binoculars. It explains more of the object you intend to view. It can also be used to identify the size of the binoculars. The magnification number is also called the mag specs. It is essential to get precise mag specs for any specific area or object.

Binoculars are designed to be airtight and with different layers of lenses for their oculars. Due to the number of lenses it contains, holding it carefully can be the best option as dropping the ocular can most times lead to a break of the lens and damage.

Wrapping It Up

The different parts and components of binoculars may have changed over the years, but the binoculars working principle remains the same. Now that you have some idea about how do binoculars work, it’s time to look for the best binoculars for you.


1. What is the interpupillary distance adjustment for?

Ans. The interpupillary distance (IPD) adjustment allows you to adjust the distance between the two eyepieces to match the distance between your eyes. This ensures that you see a single, merged image without any double vision for comfortable and immersive viewing.

2. What is the field of view in binoculars?

Ans. The field of view (FOV) refers to the width of the observable area when looking through binoculars. It is usually measured in degrees or the width in feet/meters at a specific distance. A larger field of view allows you to see a wider area and makes it easier to track moving objects or observe a broader scene.

3. What is the exit pupil of binoculars?

Ans. The exit pupil is the small, circular area of light that you see when holding your binoculars away from your eyes. It is determined by dividing the diameter of the objective lenses by the magnification power. The size of the exit pupil affects the brightness of the image. A larger exit pupil allows more light to enter your eyes so you can see a brighter image, especially in low-light conditions.

4. How do coated and fully multi-coated lenses differ?

Ans. Coated lenses refer to lenses that have received a single-layer coating on at least one surface to reduce light reflections and increase light transmission. On the other hand, fully multi-coated lenses have multiple layers of anti-reflective coatings on all air-to-glass surfaces so they offer better image brightness, contrast, and color accuracy compared to single-coated or multi-coated lenses.

About the author

Marc Niad

It’s been several years that Marc, a retired teacher and a proud dad, has silently been piling up mature bucks down the South. This humble hunter began his hunting journey at quite an early age and since then, he spent countless hours in the woods and learned good lessons in terms of woodsmanship. Along the way, he also made money sharing his skill with his followers and well-wishers.

The Ranger Expert is the brainchild of this veteran hunter who loves hunting the swamps and the hills around the Mississippi and Homochitto rivers. His most favorite hunting technique is taking his climbing gear and going to the top of pines with a 25.06 – the old-fashioned way!

He gets most of his games during late December through mid-January – his favorite hunting time. Marc strongly believes that hard work, passion, and a bit of luck can bring you success in the wild.

Leave a Comment