What do the numbers on binoculars mean?





Binoculars always come under different series name, brand name and fall under two numbers. For instance, 10x50 or 8 x 40, the initial number designates the strength of magnification. Diverse applications need various degrees of magnification.

The second number specifies the objective lens size expressed in millimeters on the lens. Size of objective lens determines how much light binocular can attain for real viewing. Larger objective lens collects more light, doubling lens diameter quadruples the light collected. Binoculars with smaller lenses are very portable and solid.


Field of View


This is normally the magnitude of an area that can be seen under the binoculars. Always, a greater magnification reduces the area that can be observed at once. Field of view can also be expressed in degrees, referred to as angular field.


Exit Pupil


Exit Pupil is the measurement of the circle of light which appears whenever you see through binoculars while holding them at a short distance from your eyes. Can also be regarded as the diameter of the definite beams of light coming from the eyepieces. It is a very important aspect in shaping how well the binoculars works in reduced light conditions. In case you hold binoculars away from your eyes and up to the light, you tend to see a bright circle right at the center of the eyepiece. The precise size can be obtained by dividing the objective lens by magnification of the binoculars.


Magnification and Lens size


The lower the magnification conveys an increased field of view. With increased magnification the field of view will be narrow. In some cases, the lower magnification is of great magnification. When it comes to the different binoculars, for instance one of 10x50, the magnification is represented by the first number.

Lens size is represented by the second number on the binoculars. The greater the lens size the weightier the binoculars. However, heavier binoculars may be awkward in certain activities. Smaller lens size might permit more portability.




Binocular lenses have optical coatings to enhance the amount of light they collect. This coating does minimize the amount of light reflected away and lost. The expensive binoculars brands will possess multiple coatings on all the lenses. These multiple lenses will assist in giving brightest and clearest images.


Levels of Coating;


•Coated-single layer on not less than one lens

•Fully-Coated-a single layer on every air-to glass surfaces

•Multi-coated-Multiple layers on not less than one lens.

•Fully-Multi-Coated-Multiple layers on every air-to-glass surfaces.


Types of prisms


Binoculars prisms come in two types, BAK-4 and BAK-7.BAK-4 prisms are denser and convey more light.BAK-7 prisms are less expense and made of reduced dense glass.


Eye Relief


Eye relief is the distance you can hold a binocular from your eye and present complete area of view. Long eye relief minimizes eyestrain and is significant to eyeglass wearers. While using binoculars with any relief of utmost 10mm you will only see the center of the image. For eye wearers consider binoculars which has an eye relief of over 16mm.