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A Bird's-Eye View

Binocular Basics

by Matt Pelikan
[from A Bird's-Eye View, August 1998 Beginning Birding Special Issue]

Along with a field guide, a binocular is about the only piece of equipment a birder needs. Any binocular is better than no binocular - but some models are better for birding than others.

Power and size: binoculars are usually described with two numbers: "8 x 40, 10 x 42." The first number is how many times the binocular magnifies what you're looking at. The second number is the diameter, in millimeters, of the large "objective" lenses through which light enters the binocular. Most birders use 7x, 8x, or 10x binoculars; which you choose is a matter of personal preference. Higher-power pairs are hard to use in the field, and lower-power models don't provide enough magnification. Birding binoculars usually have lenses between 30 and 50 mm; binocs larger than that are very heavy, and smaller ones don't admit enough light to work well in twilight conditions.

Field of view: this term refers to how wide an area you see when you look through a binocular. It is usually expressed as a field width at 1,000 yards, although some manufacturers describe the field of view as an angle. The wider the field of view, the easier it is to scan a large area or to follow a flying bird.

Roof and Porro prisms are the two basic designs of binoculars. Roof-prisms have the eyepieces and the objective lenses in a straight line; this design is more compact than the hipped porro-prism models, which have objective lenses spaced farther apart than the eye-pieces. Roof-prisms tend to be more rugged than porro-prisms of the same quality, but they are also usually more expensive. In a given price range, porro-prisms often give slightly better optical performance.

Eye relief is a measure of how far away from the binocular's eye-piece your eye needs to be. This distance is usually given in millimeters; depending on the binocular it may be from 8 mm up to 24 mm or even more. Longer eye-relief makes binoculars easier and more comfortable to use, and is especially important if you wear eye-glasses.

Size and fit: It's important to buy a pair of binoculars that feels comfortable when you use and carry it. If possible, you try out a model in the field before you purchase it. Most birders avoid pocket-sized "compact" binoculars, but for young birders with little money and small hands, a pair of compacts may be a good option. At the other extreme very large binoculars may be too ackward to carry for a full day of birding.

Price: As with most things, you get what you pay for with binoculars. Most cheap binoculars (less than $80) simply don't work well enough to do the job in the field. At the other extreme, some models cost around a thousand dollars. These are incredibly rugged and give amazing, sharp images - but few beginners are able or willing to pay that much. Many beginning birders spend between $100 and $250 for their first pair; if you shop around, you can find binoculars in this price range that will serve you well.

About the author: Matt Pelikan is editor of Winging It, the newsletter for ABA members. Before that he was the editorial advisor and author of a regular column on birding optics for A Bird's-Eye View. He lives on the island of Martha's Vineyard.