We all know that binoculars are used to get a closer look at things, to make faraway objects appear closer. Curious people want to dig a little deeper and want to know exactly how binoculars do what they do so we are going to examine the inner workings of binoculars to give you a better idea of exactly what is going on when you look through the lenses.
The first thing that most people will notice about a pair of binoculars is the lenses. The lenses take in the light and magnify the images. A pair of binoculars will usually be described with two numbers like 7×25 or 8×50 for example. The first number refers to the magnification so an 8x would make whatever you are looking at appear to be 8 times larger. The second number refers to the diameter of the objective lens. So an 8×50 pair of binoculars would have a large objective lens that is 50 millimeters in diameter.
What most people never see are the prisms that are inside binoculars. The earliest binoculars did not use prisms, they used Galilean optics which consisted of an objective lens that is convex in shape and an eyepiece lens that is concave in shape. This arrangement gives you the benefit of viewing an image that is right side up but offers a very narrow field of view and is not capable of very high magnification. Modern binoculars are constructed using Keplerian optics in which both the eyepiece and the objective lenses are convex. This allows for a much wider field of view and considerably higher magnification but using the lenses alone would create images that are upside down and laterally reversed. Prisms are used in modern binoculars to correct the orientation of the images you are viewing, letting you see images that are right side up rather than an upside down mirror image.
There are two basic designs in modern binoculars, the roof prism design or the porro prism design. Binoculars with the roof prism design can be made smaller and more compact but there may be a slight reduction in image quality when compared to porro prism binoculars. Porro prism binoculars use a larger prism and the objective lenses are spaced a little further apart giving you a better stereoscopic image. They are also less expensive to manufacture and will usually be less expensive for the end-user. The main disadvantage to the porro prism design is that they are larger and heavier.
When it comes to the inner workings of binoculars that’s pretty much all there is to it, just lenses and prisms. When purchasing binoculars of course there are many more things to take into consideration. The quality of the lenses and prisms will make a big difference in the image quality your binoculars are able to deliver. You will also want to consider things like magnification, field of view and other design elements. There are also a number of features in modern binoculars like lens coatings, image stabilization etc. To find the right pair of binoculars will take some research but if you spend a little time figuring out exactly what you need, you will be very pleased with the pair that you ultimately end up purchasing.