Binoculars are a must-have for many people who like to be outside, like bird watchers, shooters, astronomers, and hikers. They let us see details and things that are too far away for the naked eye to see.
But have you ever thought about how a pair of binos work? If you’re like me, I’ve personally used binoculars for many years before I ever started to understand how they work – this has since helped me make better purchases and understand which binos might be best for me.
Binocular Lenses and Prisms
Lenses and prisms work together in binoculars to enlarge and focus on faraway things. A pair of binoculars is made up of two telescopes that are placed next to each other. Each telescope has its own set of lenses and prisms.
Binocular Lenses
The first set of lenses, called the objective lenses, are at the front of the binoculars. They gather light from the thing you are looking at. They make a picture of an item that is upside down and backwards from left to right.
The second set of lenses are the ocular lenses – these are the lenses that you place next to your eyes and look through.
The amount of light that the binoculars can gather is based on the width of the objective lenses, which is called the aperture. The picture will be brighter and the binoculars will work better in low light if the aperture is bigger.
Binocular Prisms
The light from the objective lenses then goes through prisms inside the binoculars. The prisms, which are usually made of glass or plastic, bounce the light and send it through the eyepiece lenses. The eyepiece lenses take the picture made by the objective lenses and make it bigger and show it to your eyes in the right way.
The Porro prism is a type of prism that is often used in binoculars. It is named after the man who made it, Ignazio Porro. Inside the binoculars, the porro prisms are set up in a zigzag design. Each prism is shaped like a triangle with a right angle. They reflect the light twice, which makes the design more compact while keeping the picture in the right place.
The roof prism is another kind of prism that is used in binoculars. Roof prisms are in a straight line inside the glasses and look like roofs. They can bounce light four times, which makes them easier to make.
Magnification
The ratio between the focal length of the objective lenses and the focal length of the viewing lenses is what determines the magnification of binoculars. For example, a pair of binoculars with objective lenses that have a focal length of 50mm and eyepiece lenses that have a focal length of 10mm would have a magnification of 5x.
Field of View
In addition to magnification and aperture, binoculars are also categorized by the width of the picture that can be seen through them. This is called the field of view. When you have a wider field of view, you can see more of the area around you, which is helpful for things like bird watching and shooting.
Summary
Binoculars are made up of lenses and prisms that let us see farther away things in more detail. The objective lenses gather light, which the prisms then bounce and send to the eyepiece lenses, which make it bigger.
If you know how binoculars work, you can pick the best pair for your needs and get the most out of your trips outside.