How to Choose Binoculars

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How to Choose Binoculars

You're 300 yards from camp and you notice something moving near your tent. Is that a bush swaying in the breeze or a bear prowling for Luna bars? Binoculars can help you answer this kind of pressing backcountry question, plus identify a warbler, locate a distant trail marker or get you closer to sports action.

Getting Started

No single factor determines that one pair of binoculars is superior to another model. Your personal preferences and intended usage will determine which style is best for you.

When shopping for binoculars you'll discover wide price ranges on similar-looking models. The old axiom "you get what you pay for" rings particularly true with binoculars. Prices usually correspond to the quality of the optics. As you might expect, better optics mean better-performing binoculars.

Types of Binoculars

Mention binoculars and the image that usually comes to mind is a pair of traditional, full-size binoculars. (Why, you ask, are binoculars referred to as pairs? Answer: They use two parallel telescopes mounted on a single frame. This consolidated device then magnifies distant objects and draws them closer to us in stereoscopic vision.) Mid-size and compact binoculars, meanwhile, are sophisticated alternatives that have become popular more recently. Here's a quick comparison.

Full-Size (40mm and larger objective lenses):

    * capture more light and perform better in low-light situations
    * usually provide steadier images and a wider field of view
    * are best for serious wildlife viewing and for use on boats
    * are too big and heavy for backpacking

Mid-Size (30-39mm objective lenses):

    * nicely balance moderate size and above-average light transmission
    * are a good all-around choice for wildlife and sports use
    * tend to be a bit heavy for backpacking

Compact (less than 30mm objective lenses):

    * offer the lightest, smallest option for backpacking
    * work very well during daytime outdoor activities
    * can be less comfortable during extended periods of use

Understanding the Specs

Magnification Power
Binoculars are identified by two numbers. The first is magnification power, the second is the diameter of the front lenses, explained below.

Example: 7 x 35 binoculars have a magnification power of 7.

A magnification power of 7 means that an object will appear seven times closer than it would to your unassisted eye. For example, if you view a deer that stands 200 yards away from you through 7x binoculars, it will appear as though it were 28.6 yards away (200 divided by 7).

So, the greater the magnification power the better the view, right? Not necessarily. Binoculars with magnification powers greater than 10 amplify the movements of your hands, making steady viewing more difficult.

Objective Lens Diameter
The second number used in binocular identification refers to the diameter (in millimeters) of the objective lenses (those farther from your eyes). 7 x 35 binoculars therefore have objective lenses measuring 35mm. The diameter of the objective lenses largely determines how much light your binoculars can gather. If you have two binoculars with exactly the same specifications except for objective lens diameter, those with the larger diameter objective lenses will capture more light. More light means a brighter view, particularly in low-light conditions.

Exit Pupil
Measured in millimeters, this is the diameter of the shaft of light that exits each eyepiece and reaches the pupils of your eyes. This number is calculated by dividing the diameter of the objective lenses by the magnification. A 7 x 35 model, for example, has an exit pupil of 5mm (35 divided by 7). Generally, a bigger exit pupil means more light reaches your eyes, producing a brighter image. A large exit pupil also makes it easier to maintain a full image if your hands move or shake. Keep in mind that your eyes' pupil size varies from approximately 2.5mm in bright light to 7mm in low light.

Tip—For better viewing at dusk or dawn, look for binoculars with an exit pupil of 4mm or more.

Brightness
Some manufacturers refer to relative brightness to indicate the quantity of light that binoculars transmit to your eyes. The higher the relative-brightness number, the brighter the image. This specification serves as a key indicator of how much light will reach your eyes. Prism type, component quality and optical coatings all affect relative brightness.

Tip—Binoculars with high relative brightness make good choices for low-light viewing.

Eye Relief
This is the distance between each eyepiece and your eyes while the whole field of view is visible. Longer eye relief increases your comfort by allowing you to hold the binoculars away from your face. This spec is particularly useful if you wear glasses. Most manufacturers recommend that people who wear glasses should roll down the rubber eyepiece collars before viewing.

Tip—If you wear glasses, look for eye relief of 11mm or more.

Field of View
This spec tells you the width of the area (usually in feet) that you can view at a glance, 1,000 yards from where you stand. A wide field of view is best to find and identify objects such as birds. Usually a higher magnification power results in a narrower field of view.

Summary

Compact binoculars (common specs: 8 x 25, 10 x 25) provide excellent daytime viewing. They're your best option for weight-sensitive activities such as backpacking and mountaineering.

Mid-size binoculars (common specs: 7 x 35, 10 x 32) offer a happy medium of moderate weight and strong light-gathering performance. They are suitable for virtually any activity.

Full-size binoculars (common specs: 8 x 42, 10 x 50) are the best choice for wildlife viewing. They provide a wider field of view and greater brightness than other models.

Once you've narrowed it down by category, your choice of a particular model will then depend on your budget, intended use and individual factors such as eyeglass compatibility. Finally, remember that binoculars are only as good as they optics they use.