Ultimate Binoculars Buying Guide
Binoculars are essentially two telescopes mounted side by side to give a magnified stereoscopic view. As such, purchasing a pair can seem like Physics 101 all over again, but it doesn’t have to be. A good pair of binoculars simply offers a bright, clear view that’s easy on the eyes and a weight that’s light for your load. The difficulty is in determining which factors are most important to you, since choosing quality in one often means diminished quality in the others–or a higher price tag.
If you are looking for binoculars for a specific use, I recommend you check out the following resources:
Running the Numbers
Knowing what the numbers mean is the first order of business when it comes to purchasing binoculars. From there you can begin to understand the optical features’ interrelationships.
Field of View
The field of view is the size of the area viewed through the lens. This measurement is given either in terms of linear feet viewed from 1,000 yards or in degrees of field (1 degree of field equals a view of 52-1/2 feet from 1,000 yards). Standard binoculars range from approximately 250 to 600 feet, or roughly 5 to 11 degrees. When manufacturers talk about “flat field,” they’re referring to a sharp, clear image across the entire field of view.
Binoculars are usually labeled with a two-number code, such as 7 x 35. The first number in the code represents magnification; so 7 x 35 binoculars magnify images to seven times what would be seen by the naked eye. Most binoculars’ magnification powers range from 7 to 10. As magnification increases, field of view generally decreases.
The determining factor for the amount of light captured in an image, aperture (from the Latin aperire, “to open”) is the second number in the two-number code. It represents the size of the object (or front) lens. For example, a pair of binoculars labeled 7 x 35 would have an object lens with a diameter of 35 millimeters. Most recreational binoculars range from 20 to 60 millimeters. A large-object lens will increase clarity and is especially ideal for low-light situations.
In addition to the aperture on a pair of binoculars, a number of features contribute to–or take away from–the brightness and clarity of the imaging. Consider these features carefully when you make a purchasing decision; the relative quality of your optics directly affects the amount of eyestrain (and, therefore, headaches and fatigue) you may experience over long periods of use.
High magnification (factor 9 or 10) generally leads to diminished image brightness.
To determine the exit pupil size of a binocular, divide aperture by magnification. A pair of 7 x 35 binoculars would have an exit pupil of 5 millimeters. On bright days, the exit pupil size will have little effect on the clarity of your image, but for low-light viewing, you’ll want a minimum exit pupil of about 4 millimeters.
Most lenses and prisms are coated to decrease reflection and prevent distortion. These are advertised as being coated, fully coated, multicoated, or fully multicoated, the latter offering the best brightness and clarity.
The highest quality prisms are made with high-density BAK-4 glass, giving optimal clarity and brightness.
For focusing purposes, most binoculars feature a centrally mounted wheel or lever that adjusts both eyepieces simultaneously, and some have a focusing devise on one of the eye tubes that will compensate for differences in the strength of each eye. Pay attention to the near focus, which refers to the shortest distance from which an object can be viewed with complete clarity. This feature is especially important to bird watchers who normally prefer a near-focus factor of 13 feet.
Porro-prism binoculars are the traditional-looking binoculars in which the eyepieces are closer together than the object lenses. Although they offer a wider field of view and tend to be less expensive, Porro-prism binoculars are usually among the bulkiest and most fragile models available. The sleeker, more modern-looking roof-prism binoculars have eyepieces that are in line with the object lens, resulting in compact and durable binoculars. And finally, binoculars with reverse Porro prisms have the object lenses closer together than the eyepieces–a design that is commonly used in compact binoculars.
Water: A water-resistant and waterproof outer casing protects the instrument from rain or submersion. If you plan to use your binoculars on or near water, or in potentially wet conditions, this feature will go a long way towards preserving your binoculars’ integrity.
Construction: Some binoculars are designed to take a beating while others are quite delicate and must be handled with care. Binoculars constructed from polycarbonate/foam and aluminum are designed to be rugged yet lightweight.
Extras for Eyeglasses: Most binoculars are fitted with rubber cups on the eyepieces to position the pupils at an optimal distance from the lenses. These cups will generally fold down for users who wear glasses.
Binoculars can weigh anywhere from less than 1/2 pound to 5 pounds or more. The aperture is one of the chief weight-determining factors (because of the size of the object lenses), and binoculars with a large field of view tend to have bulky designs. Prism style and construction can also affect heaviness.
The importance of the weight factor depends on your prime uses. Most backpackers will want a small, lightweight pair of binoculars that can easily fit into a pack or pocket. Bird watchers who generally take only day hikes can afford a heavier, bulkier pair–1-1/2 to 2 pounds. Portability isn’t as much of a consideration for backyard birders or sport spectators who simply want a close-up view of the action.
Pricing It Out
Prices for binoculars range from $30 to over $1,000, so you should first determine how much you can afford before considering all the options. Once you decide how much you want to spend, look at the binoculars with the highest-quality optics–glass, prisms, and coatings–available in your price range. From there, you should narrow your choices based on the features that are most important to you: magnification, design, construction, weight, and warranty.
To clean your new binoculars, you’ll want to take special care not to rub in any abrasive particles that might scratch and distort the lenses or remove their optic coating. Use a squeeze blower or a soft hair lens brush to dust the glass surfaces. Then clean with a microfiber lens cloth or tissue to remove oils and smudges, and stash them safely in their carrying case and out of harm’s way.
Make sure to also check out my buying guide for telescopes.