How to Choose Binoculars

March 26, 2015

Binoculars improve our view of objects in the distance. This guide from the Bill Jackson Shop for Adventure will help bring into focus the right binocular for your next adventure:

Anatomy of binoculars

Objective lens: The big lenses at the farthest end. The diameter of each lens, measured in millimeters, determines how much light enters the binocular. The more light, the brighter the object appears.

Prism tubes: Where the inverted and reversed image is corrected for the eyes. There are two kinds of designs: roof and porro. Roof is sturdier and allows for a slimmer tube. Porro provides a more 3-D, lifelike image and is less expensive.

Focus control: Adjusts both prism tubes simultaneously to focus the image.

Eyepiece: Holds the eyepiece lens, where the user views the image.

Eye caps/cups: Adjusts to provide the user with “eye relief,” which is the distance from the eyepiece lens to a point in space where the image is clearly seen.

Diopter control: An adjustment dial on one eyepiece that allows the user to compensate for the imbalance between the strong and weak eye.

Understanding the numbers

Binoculars are typically identified by a series of numbers. A 7×50 6.4 binocular, for example, has a magnification power of 7, 50-millimeter diameter objective lenses, and a 6. 4-degree field of view. The larger the magnification number, the larger the image will appear. The larger the objective lens, the brighter the image will appear. The larger the field of view, the wider range the user can view.

Other terms

Magnification/power: A number that represents how much closer an object will appear than if using the unassisted eye. For example, if a seabird is 300 yards away and viewed through an 8x binocular, the bird will appear as if it were 37.5 yards away (300/8=37.5).

Exit pupil: The round white image reflected on the eyepiece. For proper light-gathering potential, the diameter of the binocular pupil must be equal to or greater than the diameter of your eye pupil during various lighting conditions.

An exit pupil diameter of at least 5 mm is recommended for most viewing situations.

Field of view: The width of the area, measured in feet, that the user can see at a glance, 1,000 yards from where he is standing. The higher the magnification, the narrower the field of view.

Lens coating: Some light that enters a binocular is reflected, thus reducing the amount of light that ultimately goes to the eyepiece. Less light, a darker image. To combat this, manufacturers apply coatings to the lenses to ensure sharp, bright images.

Usage

How, where and when you use your binocular helps determine your needs. Some adventurers do their viewing in bright light, so small, compact binoculars suit them well. Viewing at dawn, dusk or night requires full-size binoculars that take in more light. Adventurers using binoculars in adverse conditions will want to take into consideration waterproofing, anti-fogging and shock resistance.

Some guidelines to determine which binocular is best for your usage:

Outdoors viewing (Camping, hiking, hunting)

Magnification: 8x to 10x; Objective lens size: 30 to 56 mm

What to look for: portability and durability against the elements; compact and lightweight; waterproof, rubberized exterior for better grip; large objective lens for low-light conditions (early morning, dusk).

Birdwatching/nature viewing

Forest, woods: Magnification, 8x to 10x

Lakes, wetlands: Magnification, 8x to 12x

Objective lens size: 30 to 56 mm

What to look for: compact, lightweight, wide field of view.

Marine sports/fishing

Magnification: 7x to 10x; Objective lens size: 50 to 70 mm

What to look for: waterproofing, durability; large objective diameter; wide field of view.

Spectator sports

Fast sports: Magnification, 7x to 10x

Outdoors: Magnification, 8x to 12x

Medium stadiums: Magnification, 4x to 8x

Large stadiums: Magnification, 8x to 10x

Objective lens size: 25 to 50 mm

What to look for: wide field of view; zoom models allow for best, most convenient viewing.

Traveling

Closeup: Magnification, 7x to 10x

Landscapes, buildings: Magnification, 4x to 8x

Objective lens size: 21 to 30 mm

What to look for: compact, lightweight.

Stargazing

Magnification: 7x to 10x; Objective lens size: 40 to 50 mm

What to look for: large objective lens.

Maintenance and storage

Use only quality binocular-cleaning products sold by your retailer, otherwise you may damage the lens.

Avoid extended exposure to high humidity, high temperatures and dusty areas.

In order to prevent mold, wipe the binocular off with a dry cloth and store in a cool, dry place.

Waterproof models are airtight and not likely to allow mold to grow. However, it is important to rinse well if exposed to seawater or mud, and wipe dry.

Always remember to clean the lens with a lens cleaner and wipe dry with a lens cloth.

Brands of binoculars carried by Bill Jackson’s:

Nikon

Swarovski

By Rich Kenda