How Do Binoculars Work

How Do Binoculars Work?

Just like other discoveries, binoculars are an idea that once became a reality. With its roots dating back to the 1600s, this brilliant invention underwent numerous improvements that made it what it is today. For instance, a French inventor J.P. Lemiere applied for a patent for the binoculars in 1825. However, in 1854, a major breakthrough was evidenced after Ignacio Porro patented the Porro prism, which became the major breakthrough for the success of the modern binoculars. So, how do binoculars work? This is one question most people keep asking whenever they use these tools to visualize objects that are far away from their vicinity.

Now, binoculars are interesting tools that work brilliantly. They allow us to view and magnify distant objects which otherwise would strain our eyes and muscles whenever we attempt to view them. At first, binoculars were designed by combining two telescopes together to create a monocular image.

However, following numerous technological improvements, especially with the discovery of the Porro prism system, different variations of binoculars have emerged ranging from the smallest devices used in concerts and operas to large-sized binoculars used in the military especially by snipper spotters.

So, having said that, let’s now get to our main topic of the day which is discussing how binoculars work.


How Do Binoculars Work: Step-by-Step Guide


Consider this Simple Concept


So, before we cover how binoculars work, I will first explain a simple concept that will demonstrate how telescopes work. After this, everything else in this topic will pretty much be easier to process.

Here, you’ll need two magnifying glasses and a piece of tracing paper. So, start by lighting a candle on one side then place the magnifying glass at the center and the tracing paper at the back. When you look at the image, you’ll realize that it’s inverted.

If you take another magnifying glass and place it in front of the tracing paper, then it will act as the eyepiece while the magnifying glass at the center will act as the objective lens. What you’ve just made is a telescope that is perfect for viewing the solar system (since there’s no issue with the inverted images).

But, when it comes to binoculars, a little adjustment will need to be made at the center to make the images upright and easy to process. So, here, Porro prisms will need to be added between the objective lens and the eyepiece to erect the candle image and make it upright for easy viewing.

So, with that short simple concept, let’s get started.

Briefly, binoculars are made up of three key parts which are;

  • The eyepiece or the ocular
  • The prisms
  • And the objective lens

Objective Lens


The objective lenses are the collection lenses that are located on the front section of the binoculars. These lenses can either be small or large depending on your needs. Their main function is to gather light from the object being focused to make it easier for processing.

One rule you need to understand though is that the larger the aperture—the diameter of the objective lens, the brighter and sharper the resulting image will be. This, therefore, mean that the larger the binoculars are, the stronger they are in terms of gathering light hence the more efficient they tend to be.


The Prisms


Next to the objective lens, there are the prisms. Earlier on in our demonstration, we discussed how the objective lens inverts an object being focused (the candle) to make it appear upside-down. Since binoculars are designed for viewing objects from far, this problem is easily handled by adding these special prisms in the equation.

Briefly, prisms are solid glasses that function as the mirrors in the binoculars. The only difference between them and ordinary mirrors is that they actually don’t reflect the background. Their main purpose, therefore, is to correct the upside-down orientation of an image that has been captured by the aperture.

So, how do they manage this? First and foremost, the prisms are two and are placed adjacent to each other. When an image is captured by the objective lens, it goes through the first prism which flips it at an angle of 90° before sending it to the other prism. In the next prism, the image is then flipped at a further 90° angle before it’s released to the eyepiece.

This back and forth flipping of the image results to a 180°turn which makes the image upright by the time it’s exiting through the eyepiece.

Following the advancement in technology, different types of prisms have been developed two of which are the Porro and the roof prisms.

  • Porro Prisms:

With this type of prisms, each one of them is set at a right angle with each other. When an image is transacted, it hits the top and bottom of the first prism then hits the left and right sides of the second prism before it finally exits through the eyepiece.

Binoculars using the Porro prism principle are easy to manufacture and therefore affordable. The only downside is that they’re less powerful hence the best for basic civilian use.

  • Roof Prisms:

These prisms are as a result of latter technological improvement that has been done on the binoculars to make them smaller without sacrificing image clarity and efficiency.

Although they function in the same way as the Porro prisms, they have a more elaborate production requirement, as the prisms are placed closer together to enhance image clarity.

These binoculars are smaller and are more powerful making them the best for demanding activities such as military operations.




Finally, we have the eyepiece. This part of the binoculars is the one located closest to the eyes. The lenses here are the ones we look at when viewing an image as they’re the ones responsible for processing the object making it easier to be interpreted by the eyes.

Eyepieces in binoculars usually come in two variations, which are concave, and the convex.

  • Concave Lenses: Also known as convergence lenses, these lenses are thin in the middle and thick on the edges. Their main purpose is to disperse or rather scatter light.
  • Convex Lenses: Convex lenses, on the other hand, are thick in the middle and thin on the edges. Their design makes them the best for converging light in one spot hence the name convergence lenses. Due to their converging characteristics, convex lenses are used in magnifying glasses hence the best for binoculars.


Calculating the Binoculars Magnification


Lastly, there’s the magnification, also called, the power of the binoculars. Since we don’t want to leave any tables unturned, we realized it would be best if we could explain the magnification concept to clear everything up.

Now, all binoculars have a magnification number which is basically a rating factor that defines how good binoculars are in viewing certain objects or terrains. This number is called the magnification specification and it’s denoted like “8 × 42” (just an example).

So, what do the numbers mean? Now, the first number represents the number of times an object’s size is multiplied into the lens. This can range anywhere from ×2, ×4, ×8, ×10 to ×12 among others. The second number represents the physical diameter of the objective lenses and it’s measured in millimeters.



So, there you have it all. The next time someone asks you what binoculars really are, then I believe you’ll be able to explain to them fluently without running out of words. As you can see, binoculars are structured into three parts which are the objective lens the prisms and the ocular, also called the eyepiece.

The diameter of the objective lens is the aperture and it’s the one responsible for the resolution or the sharpness of the image being gathered.

Something else about the binoculars is that the inside is tightly sealed to prevent moisture from collecting on the prisms. This can make them foggy thus compromising the image being captured. To prevent this, modern binoculars are filled with nitrogen to keep the oculars and the prisms clear while still prolonging the lifespan of the binoculars.

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