Orvis Guyer's Guide for Binoculars

Binoculars are as essential for outdoor adventure as good boots or a waterproof coat, but which pair will best suit your needs depends entirely on what they will be used for. Magnification, angle of view, brightness index, weight, focusing distance – all of these features should be carefully considered when choosing a pair of binoculars. Here are some guidelines that will help you find the right pair.


Magnification refers to the power of your binoculars to increase the size of the scene you are viewing. For example, assume you're considering purchasing 10 x 25 binoculars. The first number, 10, means that the image will appear ten times closer than it would to the naked eye. The second number, 25, is the measure in millimeters of the front lens. In general, a large lens enables you to see better in dim conditions: the larger the lens, the brighter the image. The lens also compensates for the light lost by magnification. Powerful magnification can dissipate the natural brightness of your environment.

Angle of View

Angle of view refers to the field of vision you have when looking through your binoculars. The angle is measured in degrees, and the larger the angle of view, the easier it will be to spot a subject. A wide-angle binocular has an Apparent Angle of View of 65 degrees or greater.

Brightness Index

Those who plan on using their binoculars at a range of times during the day and in a variety of light conditions should be aware of the brightness index. The exit-pupil diameter is used as a way to measure the brightness of an image; this number is reached by dividing the objective lens diameter by the magnification power. Binoculars that are 10 x 42 binoculars have an exit pupil diameter of 4.2mm (42 divided by 10). If you plan on using your glasses in the daytime exclusively, an exit pupil diameter of 2-3 should suffice. Those who want the view wildlife at dawn or dusk will need to purchase a pair of binoculars with an exit pupil diameter of at least 5-7mm.

Consider the Conditions of Use

The weight, shape, and weatherproof capacities of a pair of binoculars is a matter of personal preference. That said, binoculars for a rainforest trip or boating use should always be water-resistant to avoid disappointment.

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