Technology and the Science of Lenses and Optics in Binoculars

The easiest way to describe binoculars as two telescopes, one for each eye, that have been stuck together in one convenient unit. However, this might be not be the most helpful explanation, especially if a person does not know how telescopes work. This article will seek to explain how such a device works in the context of binoculars.

Types of Lenses

A convex lens is a piece of glass that has been curved so that the outside edges are thicker than the middle of the glass. When light hits this piece of glass in its middle, it is forced to slow down and bend. This allows the glass to take objects that are far away and make them appear as though they are closer than they actually are.

A concave lens is a lens that is thicker around the edges and thin in the middle. This causes light, when it enters the lens, to spread out around the edges like how a firework expands. This allows light to cover a larger area when it goes through the lens.

How Telescopes Work

Telescopes are specifically intended to magnify the image of an object that is in the distance. Inside of a telescope’s casing, there are two convex lenses. The first lens takes the light that comes in and captures that image right behind the second lens. It is known as the objective lens because it is focused on the object that is being looked at. The second lens captures the image that is inside of the telescope and makes it bigger.

How Lenses and Prisms Work in Binoculars

Because binoculars are basically two different telescopes that are attached so that they are side by side, there is one for each eye. The main problem with just the two lenses is that the rays, when passing through a lens that is considered to be convex, is that sometimes the images become flipped upside down since the rays are crossing. In order to fix this problem, there are two chunks of glass in each telescope that are put into the binocular.

These wedges are known as prisms that take the image and cause it to flip upside down 180 degrees. The first prism will flip the image by 90 degrees. The second will flip it an additional 90 degrees. These prisms can be located at 90 degree angles from one another, which is known as a Porro formation. They can also be located back to back, which is called the roof prism formation.

Prisms are what makes the binoculars heavy because they are such large wedges. The reason why field lenses are lighter than binoculars is because they only use lenses to flip the image upside down. Because prisms are not used, the image that is produced by field glasses tends to be of a poorer quality.

How do the Numbers Work?

Binoculars tend to have a set of numbers that are separated by an “x” on them.

  • The first of these two numbers describes how many times closer the image will be. If there is a five for the first number, then the image will be five times closer.
  • The second number is the size of the objective lens, which describes the size of the image that is able to be captured.

This brief overview of field glasses provides a basic explanation of the science of binoculars and an introduction to how optics work within binoculars . More information can be found at and