Understanding How Binoculars Work

Binoculars are a vital piece of equipment that can enhance daily activities such as hunting, birding, hiking, and sporting events. Primarily binoculars take a distant image, enlarges it through a series of lenses for viewing; while remaining small and light enough to be mobile. Within this article, the series of lenses in a pair of binoculars will be examined while explaining how they work to produce a magnified image.

Binoculars for the most part are built fairly straight-forward and simple. There are the lenses at the end of the optical tube called the objective lens. The objective lens which is measured in millimeters, gathers light and focuses the light on the ocular lens. The ocular lens is the small lens in the eyepiece. Binoculars are really two small scopes mounted side-by-side so the user can view the desired image with both eyes instead of just one eye.

When inspecting a pair of binoculars, there are two numbers the individual will notice which are expressed as 10x42mm or something similar. These numbers describe the binoculars capabilities. For example, the first number (10) in 10x42 is the magnification, this will magnify the image ten times the images normal size. Note: in most cases, the stronger the magnification, the smaller the field of view will be. The second number (42) in 10x42 in the aperture. The aperture is the size of the binoculars objective lens. The aperture is measured in millimeters, the larger the aperture, the more light is gathered. The smaller the aperture, the less light is gathered. Further more, the two numbers can also express the exit pupil.

The exit pupil is the amount of light rays that enter the objective lens and exits the ocular lens. The measurement of the exit pupil is achieved by dividing the aperture lens size by the magnification size. For example, the Nikon 10x42 Monarch Binocular, the exit pupil would be found by dividing the aperture (42) by the magnification (10), equaling 4.2 exit pupil. A higher exit pupil means the binoculars will work efficiently in dim light. For well-lit surroundings, an exit pupil of 2.5 to 4 is sufficient. If the individual holds a pair of binoculars at arms length, they will be able to clearly see the circle of light in the eyepiece, representing the exit pupil. In-between the aperture lens and the objective lens is the prism.

There are two types of prisms in common use, porro-prism and roof-prism. The porro-prism binoculars can be identified by their offset tubes; the objective lenses are not lined up with the ocular lenses, the ocular lenses are usually closer together than the objective lenses, but the opposite can also be true, particularly in compact models. The porro-prism binoculars are usually optically superior to the roof-prism binoculars, especially in medium priced class binoculars. Porro-prism binoculars have a single pivot between the two halves of the binoculars, therefore easier to adjust for the inter-pupillary (distance between the eyes).

Roof-prisms are basically in-line inside the optical tube, this makes for a more compact set of binoculars. Roof-prism binoculars have straight tubes (the objective lens is in-line with the ocular lens) which makes them more compact. The roof-prism binoculars usually have two pivot points between the tubes and are a little more difficult to adjust for the inter-pupillary (distance between the eyes).

The components of binoculars, such as the optics have changed over the years, but the basic construction of binoculars and how they work has remained unchanged. All binoculars still have three major components. The objective lens which collects light and focuses that light in the users eyes. A set of prisms which invert the image, turning the image right-side up, and the ocular lens that magnifies the image. With this information on individual will have the basic knowledge on how binoculars work and will more easily decide on what type of binocular is right for him or her.

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