How Do Binoculars Work? Learn How Binoculars Work | Terms Glossary

how do binoculars work
How do binoculars work, you ask? Learn how binoculars work with explanations of roof vs porro prism, FOV, magnification ranges, objective lens diameters & more!

It’s a question people don’t often ask themselves: how do binoculars work? In this day and age, where technological advancements are happening every day, we take a lot of the world around us for granted. We use televisions, cell phones, microwaves, and laptop computers without ever questioning how they are able to do what they do.

But sometimes our curiosity gets the better of us, and we simply need to know.

With sports optics, it’s important to answer the question of how do binoculars work. It’s important because when you go to the store to buy a pair, you have to browse through a gigantic selection. By knowing more about how they work, you can have a better chance of choosing the perfect specs for your needs.

How Do Binoculars Work: Roof and Porro Prisms

You don’t need to have an advanced degree in physics to understand how binoculars work. All you need to know is that light is capable of bending and curving when it passes through an object. Once you can wrap your mind around that basic principle, the rest is easy as pie.

Most binoculars use prisms along with lenses to enhance the image’s color, quality, and size. The light enters the lens, gets reversed and magnified through the prisms, and eventually enters your eyes. And believe it or not, your eyes are also binocular instruments. This means they take two images and bring them together to form a single, high quality image.

The two most common types of binocular prisms are roof and porro.

  • Roof Prism Binoculars – These use small prisms—hence the compact nature of the binoculars in which they are found. They are much lighter than those used in porro prism models, too.
  • Porro Prism Binoculars – Using prisms that are designed in a double-Z shape, these binoculars need more room to house the inner workings. This means that porro prism binoculars are generally bigger and heavier than roof prism ones. But they are also far cheaper.

How Do Binoculars Work: A Glossary

You need to know the terminology of binoculars if you want to make an informed decision about which pair you should buy next.

To help you get a handle on the lingo, here’s a glossary of various terms you’re bound to run into.

  • Coating – In the form of aluminum, magnesium, fluoride, silver, dialectric, and others, coatings are put on lenses for a variety of reasons. Sometimes it’s for anti-reflection properties and sometimes it’s for water-repellence. Multi- and fully-coated lenses offer the highest quality images.
  • Eye Cups – Usually made from rubber, these are the attachments on the binoculars’ eye pieces that allow you to position your eyes at a reasonable distance from the glass. Fold-down and twist-up are two types of eye cups.
  • Eye Relief – This is the distance light travels from the eye piece lens to your eye, measured in millimeters.
  • Exit Pupil – The amount of light that enters the objective lens and exits the ocular lens (eye piece). It can be found by dividing the objective lens diameter by the magnification. (Example: in a pair of 10×40 specs, the exit pupil would be 4)
  • Field of View – This is the amount of space you can see through your binoculars. Measured in feet, the Field of View refers to how much you can view standing 1,000 yards away.
  • Magnification – How many times an object is enlarged by looking through your binoculars. (Example: a pair of 10×40 specs would magnify an object 10 times its natural size)
  • Objective Lens Diameter – This is the size of the lens the light first travels through. The bigger the objective lens, the more light that can enter. This is measured in millimeters. (For example: a pair of 10×40 binoculars would have an objective lens diameter of 40mm)
  • Prism – This is what the light travels through after entering the objective lens. Generally, binoculars come in two different prism types: roof and porro.

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