How do binoculars work?

Binoculars belonging to a Congressional Medal of Honor winner
© Minnesota Historical Society (Flickr)
What are Binoculars?
Binoculars are, in essence, two telescopes mounted side by side in a hand-held device. However, unlike telescopes, binoculars are designed to be views using both eyes simultaneously. This configuration allows greater depth and perception from the image as the human brain is able to more accurately reproduce the stereoscopic view which it usually receives from the eyes.

How do binoculars work?
But how do binoculars work?

Traditionally, binoculars used a simple single lens configuration, in which light passed through a primary lens reducing the resulting image in size by a factor of one, before passing through glass eye pieces and into the human eye for processing.

However, these field binoculars were super seeded when prism glasses were first designed. These new small binoculars are made up of a series of lenses, prism glasses, and eye pieces.

The incoming light passes simultaneously through the first lenses, magnifying the image before passing it to a second series of lenses. Depending on make and model of your binoculars, as well as cost, your field glasses will have between two and four sets of lenses, which are used to increase binocular zoom. It is also possible that you may have image stabilizer binoculars, which use electronic devices to reduce image shake from hand movement etc. For each set of lenses present within the body of the binoculars, the image becomes more magnified and clarified. Often binoculars, especially those designed as naval binoculars, theater binoculars, astronomical binoculars and binoculars for birding are equipped with a focusing mechanism, which tilts and alters the angles of the internal lenses to alter the image produced before it enters the human eye, correcting for any eye sight deficiencies.

Two pairs of prisms within each barrel of your binoculars flip the images before sending the light to the eye piece, ready for the image to be processed by the human brain. The main purpose of these binoculars is to reduce the size and weight of the binoculars body.