A.N.T.S

1. Understand the numbers. Binoculars are referred to with 2 numbers, such as 7 x 35 or 10 x 50. The number before the "x" is the magnification factor, or power; the 7 x 35 lenses will make objects appear 7 times closer, while the 10 x 50 lenses will make objects appear 10 times closer. The second number is the diameter of the main (objective) lenses in millimeters; 7 x 35 lenses are 35 millimeters (1.38 inches) in diameter, while 10 x 50 lenses are 50 millimeters (1.97 inches) in diameter. Dividing the second number by the first yields the exit pupil value, or the diameter of the light beam that reaches your eye in millimeters. (For both example lenses, 35 divided by 7 or 50 divided by 10, is 5 millimeters.)
   • The higher the magnification, the dimmer the image, and while the image you see will be larger, your field of view will narrow, and consequently, you'll find it harder to keep the image focused. If you choose binoculars with 10 x magnification or greater, get a pair with a tripod socket so you can mount and steady your binoculars when needed. If you need a wide field of view, choose a lower magnification.
   • The larger the objective lens, the more light it can gather, which is important in low-light activities such as astronomy or hunting at dawn or dusk. However, the larger the lenses are, the more the binoculars will weigh. Generally, most binoculars have objective lenses with a diameter of 30 to 50 millimeters (1.18 to 1.97 inches), with compact binoculars having lenses 25 millimeters (1 inch) and under and astronomical binoculars having lenses larger than 50 millimeters.
   • The larger the exit pupil, the more light that reaches your eyes. The human eye dilates from 2 to 7 millimeters, depending on how little light is available. Ideally, you should shoot for an exit pupil value that matches the width your eyes dilate to.
2. Consider the lenses. Most binoculars have glass lenses, which generally provide better image quality, but often cost more than plastic lenses. (However, a set of plastic lenses that provide the same image quality as a set of glass lenses will cost more.) Glass also partially reflects the light hitting it, but this can be compensated for with the right coating.
   • Lens coatings are described with the following codes: C means that only some surfaces have been coated with a single coating layer; FC means that all glass lens surfaces other have been coated; MC means that some surfaces have been coated with multiple layers; and FMC means that all glass lens surfaces have been coated with multiple layers. Multiple-layer coatings are generally superior to single coatings but add to the cost of the binoculars.
   • Plastic lenses, while generally of poorer image quality, are more rugged than glass lenses and should be considered for situations where durability is important, such as mountain climbing.
3. Evaluate the eyepieces. The eyepiece lenses should rest a comfortable distance from your eyes, and even further if you wear glasses. This is called "eye relief" and normally ranges from 5 to 20 millimeters (0.2 to 0.98 inches). If you wear glasses, you'll need an eye relief of 14 to 15 millimeters (0.55 to 0.59 inches) or greater, as most eyeglasses rest from 9 to 13 millimeters (0.35 to 0.5 inches) from the eye.
   • Many binoculars include rubber eye cups around the eyepieces to help you seat the eyepieces over your eyes when using the binoculars. If you wear glasses, look for binoculars with eye cups that retract or flip out of the way.
4. Test the focusing ability. Look at how closely you can focus the binoculars in the store and measure the distance between them and the object you're looking at.
   • Binoculars focus in one of 2 ways: Most binoculars have a center-post mechanism, along with a diopter corrector to allow for one of your eyes being stronger or weaker than the other. Waterproof binoculars, however, usually have individual focusing for each lenses, with controls on each eyepiece.
   • Some binoculars are "focus-free," with no ability to adjust the focus whatsoever. These binoculars can cause eyestrain if you attempt to focus on something closer than the pre-set distance.
5. Look at the prism design. Most binoculars have their main lenses spaced wider than the eyepieces, thanks to the Porro prisms they use. This makes the binoculars larger but makes nearby objects appear more 3-dimensional. Binoculars that use roof prisms let the main lenses rest in line with the eyepieces, making the binoculars more compact but usually at the cost of image quality. However, roof prism binoculars can be made to deliver images of quality equal to Porro prism binoculars but at greater cost.
   • Less expensive binoculars use BK-7 prisms, which tend to square off one side of the image, while more expensive binoculars use BAK-4 prisms, which deliver more light and sharper, rounder images.
6. Decide how heavy a pair of binoculars you can handle. As noted, high-magnification and large-lens binoculars weigh more than standard binoculars. You can compensate for the weight and stabilize the binoculars by mounting them on a tripod or with a strap that lets you carry them around your neck, but if you plan to travel long distances, you may want to settle for less powerful but lighter binoculars.
7. Consider waterproof versus water-resistant. If you don't plan on using your binoculars in bad weather or in conditions where they'll get wet very often, you can get by with water-resistant binoculars. If you plan to take them along whitewater rafting or skiing, get waterproof binoculars instead.
8. Look at the manufacturer's reputation and guarantees. Consider how long the manufacturer has been in business and what other optical products they make, if any, as well as how they'll handle matters if the binoculars get damaged.

Tips

• Some binoculars have the capability to view images in a range of magnifications, letting you take in an entire scene or zoom in to your favorite part of it. Note that as you increase the magnification, your field of view will narrow and you'll find it harder to stay focused on the image.
• Some more expensive, high-magnification binoculars include built-in stabilizers to help you stay focused on an image. Generally, these binoculars cost $1,000 or more.

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