Parts of Binoculars and Their Functions

Binoculars are a pair of two telescopes mounted side-by-side and aligned to point in the same direction which allows the viewer to see magnified distant objects with both eyes while looking through them. They are the second most popular optical devices used in the world besides glasses.

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They are used for different purposes. Some of the popular uses of binoculars are military applications, the military used them both in the sea and inland for various security applications. These devices are also used by nature enthusiasts; which include hobbies such as hunting, bird watching, hikers, astronomers, and among others.

parts of binoculars

But before we look at the parts of binoculars and their functions, let’s see how these devices have evolved.

Binoculars over the years have evolved. From Galilean glasses to the modern binoculars we see today. Their fundamental structure has not changed much except some few improvements and add-ons that some recent day binoculars have such as lens and prism coatings, gas purging in the binoculars interior and stabilization techniques used to stabilize high magnification binoculars.

 A quick Lists of the Parts of Binoculars

  1. Objective Lenses
  2. Eyepiece Lenses
  3. Prisms
  4. Focus wheel
  5. Diopter
  6. Chassis

Below are the detailed roles each part plays in the proper functioning of the binoculars.

Objective Lenses

The objective lenses are located directly opposite the eyepiece lenses and are the furthest from the user’s eyes when viewing. They are noticeably bigger than the eyepiece lenses. Their diameter determines how much light the binoculars are able to gather from the target. They capture the available light and then direct it to the eyepiece which allows the viewer to see the object.

These days you will find many manufacturers use coatings on them to enhance the light transmission. These coatings vary from partial to fully multi-coated. The more coatings that are applied the better the optical performance of the binoculars.

It is always vital to ensure these lenses don’t get damaged otherwise, they will render the binoculars useless as they are the ones that provide the main insight of your target.

This part of the binoculars also determines how big or small your binoculars might look or feel. As the size of the objective lens affects the weight of the binoculars. The bigger the objective lens, the more light is able to gather from the target.

For example, Binoculars marked 8 x 42. Has an objective lens diameter of 42mm and magnification of eight times(  8 x ).

Eyepiece Lenses

These lenses are closest to the viewer’s eyes when you look through your device and are noticeably smaller than the objective lens. When the objective lens collects the light and brings it to focus creating the image, the eyepiece which is placed near the focal point of the objective lens then magnifies the image.

The amount of magnification depends on the focal length of the eyepiece. Eyepiece consists of several lens elements in a housing. The image can be focused by moving the eyepiece nearer or further from the objective lens. Most binoculars have a focusing wheel to allow you to move the shaft in which the eyepiece is mounted without having to manipulate the eyepiece directly.

This part of the binoculars is usually permanently mounted in the binoculars. which causes them to have pre-determined magnification and field of view. However, they are also interchangeable. When this is done the magnification could either be reduced or increase while also altering the field of view as well.


when the objective lens gathers the light and creates the image when it gets to focus on the eyepiece it will be viewed as inverted image and to correct the inverted image, prisms are introduced in between the objective lens and the eyepiece to correct the image orientation. Maybe for some applications, it might not be necessary but for others, it might be an issue.

parts of binoculars

The prisms are also responsible for making the binoculars smaller enough to be held in the hands. This is as a result of their path bending qualities, as the light’s path curls through the prisms, the length of the instrument is reduced making it easier to handle

Binoculars are classified into types by the type of prism used inside them. The two most common type of binoculars are the roof prism binoculars and Porro prism binoculars. The two are identified by their shapes. The roof prism binoculars have a straight sleeker shape while the Porro prism binoculars have a dog leg like shape.

Focus Wheel

The focus wheel is often located near the eyepiece. It can either be in between the lenses or on one of the eyepiece.

When the focus wheel is in the center, its called center focus and when it is in the side, it is either left or right focus binoculars. The purpose of the focus wheel is to slightly move the interior lenses of the eyepiece to bring the image into focus.

It is important especially for those who wear glasses as this will help them adjust the binoculars to get sharper images.

You will find binoculars in the market that are also called self-focusing binoculars – not often recommended for eyeglass wearers because they rely on the strength of the viewer’s eye to bring the image to focus.

Diopter Knob

The diopter knob is a ring that is directly situated behind the eyepiece lenses. You will find the knob on one of the oculars which can either be turned to the right or left. It permits you to individually focus the eyepiece lenses. This is to compensate for the differences in the eye strength of the user. Mostly useful for those wear glasses.


The chassis is the housing that is holding all the parts of the binoculars together in one unit. Different manufacturers use different materials to create the body of the binoculars. Some are lightweight and durable, others have more strength. Depending on the type of material used for the body, it can affect the weight as well as the longevity of the device and how much harsh weather conditions it can endue with damage.





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