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Binoculars: How to Choose

The Basics of Binoculars When shopping for binoculars you'll discover wide price ranges on similar-looking styles. The familiar bromide "you get what you pay for" rings particularly true with binoculars. Prices usually correspond to the quality of the optics. As you might expect,

Binoculars: How to Choose

The Basics of Binoculars

No single factor determines that one model of binoculars is superior to another. 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 styles. The familiar bromide "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 images that usually comes to mind are traditional, full-size binoculars. 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 binocular option for backpacking
  • work very well during daytime outdoor activities
  • can be less comfortable during extended periods of use

Monoculars (single scopes):

  • offer the smallest and usually lightest option for viewing distances
  • single-eye viewing is usually desired only for short-term usage

Understanding the Specs

Magnification Power 

Binoculars are identified by 2 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 7 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; those closer to the "object" being viewed). 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 2 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 

Exit pupil is a number that indicates how bright objects will appear when viewed in low-light situations. A higher number means brighter images.



Point your binoculars at a light source, hold them about a foot in front of your face and peer into either eyepiece. See a small, bright dot? That circle of light is known as the exit pupil—the opening that permits light to exit each binocular barrel and reach the pupils of your eyes.

Exit pupil size (measured in millimeters) is calculated by dividing the diameter of the objective lenses by the magnification number. For 7 x 35 binoculars, for example, 35 divided by 7 equals 5.

The wider the diameter of the exit pupil, the more light that can pass through, resulting in brighter, easier-to-see images when lighting is poor. If you anticipate regularly using binoculars in low-light situations—at dawn, dusk, within dense tree cover or while observing the night sky—seek out models with a high exit pupil number, preferably 4mm or higher. Often exit pupils of that diameter are found only in full- or mid-size binoculars. The tradeoff of such units: more bulk and weight.

For standard daylight viewing, exit pupil numbers are less important. In bright light human pupils narrow to roughly 2mm. All binoculars, compact models included, offer exit pupils that size or larger.

In dim light, however, our pupils can widen up to 7mm. A 7 x 50 binocular, for instance, offers an exit pupil size of 7.1mm—a good choice for low-light viewing. A large exit pupil also makes it easier to maintain a full image of an object if your hands move or shake.

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

Relative Brightness



Relative brightness is determined by squaring the exit pupil number. For example, a 10.5 x 45 binocular offers an exit pupil of 4.3. Square that number (4.3 x 4.3) and arrive at a relative brightness number of 18.5. The higher the relative-brightness number, the brighter objects will appear to your eyes.

Do identical exit pupil size numbers produce identical brightness levels? Manufacturers of high-end binoculars say no, asserting that a variety of refinements—prism type, lens elements, 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. But exceptions to this general rule do exist.

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 binocular 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. Remember that binoculars are only as good as they optics they use.

We conclude with this footnote: Binoculars are commonly referred to as "a pair of binoculars." As an REI.com reader points out, this usage is misapplied. Technically, a binocular is a pair of monoculars in 1 assembly—2 parallel telescopes mounted on a single frame. This consolidated, 2-barrel device magnifies distant objects and draws them closer to us in stereoscopic vision.

Sourced By T.D. Wood