More than 46 million birdwatchers spend almost $500 million annually on binoculars and related equipment in the U.S., according to the federal Fish and Wildlife Service. Birdwatchers aren't the only ones looking to cozy up to their subjects--boaters, hunters, sports fans, and theater-goers all rely on binoculars.

But binoculars are about more than simple magnification. Depending on how you plan to use them, you'll want to think about varying combinations of weight, power, image quality, durability, field of view, and ease of use.

Of course, price is also a factor. But surprisingly, our tests showed that quality doesn't always come with price. More-expensive models do have more-effective coatings on their optics (lenses and prisms), which sharpen the image and keep stray light from bouncing around inside the binoculars. Overall, lens and prism quality have improved in binoculars. But some models in all price categories produced images that fell short in quality, with such problems as color fringes around objects and a tendency to make straight lines look bowed.

The biggest innovations in binoculars over the last several years are the addition of image-stability technologies and digital-camera capabilities.

We tested 34 pairs of binoculars for image quality, ease-of-use, and durability (for which we devised a torture test, subjecting the binoculars to extremes of cold, heat, humidity and rain, and repeatedly hitting a table with them, swinging them from 3 feet away).


HOW TO CHOOSE

Choosing binoculars is a two-part process, based as much on what you plan to do with them as on your personal preferences.

Consider your main use for the binoculars. What you'll need from your binoculars varies a lot with how you'll use them. Take a look at our CR Quick Recommendations to determine the features that will best suit your purposes.

Choose between compact and full-sized models. Compact binoculars fit in the palm of your hand, and are a good solution to the bulky size and heavier weights characteristic of full-size binoculars. Both are equal in terms of magnification, image quality, and price. But some people find compacts harder to adjust than full-size binoculars, and if you wear glasses, they can be difficult to align. Other than that, you can choose from among narrow-set, wide-set, and in-line styles. None is better optically than the others; the style you choose is a matter of preference.

Decide on what power you need. Power represents the number of times an image is magnified by the binoculars. Most common for outdoor uses like bird-watching and hunting are 8x and 10x--the powers we rated for this report. Higher powers like 20x and beyond are preferred by astronomers, while 7x is probably sufficient for sports spectators and theater-goers.

Choose a lens size. You also need to know the diameter of the binoculars' objective lenses, represented in millimeters by the second number in binocular measurements (such as 8x42). Larger lenses allow more light to enter and provide a better image, but can also be heavier.

Consider the exit pupil. The exit pupil is the size of the disk of light formed near the eyepiece. Larger exit pupils provide more detail in dim light. An exit pupil of 5mm is optimal.

For use with glasses, note other considerations. Field of view represents the area visible through your binoculars. If you wear glasses, look for binoculars with a higher rating for field of view (with glasses). If you don't wear glasses, retractable eye cups are easier and faster to adjust than soft-rubber ones that fold back.

Check fit. Binoculars are two telescopes tied together; if not perfectly balanced, they may cause eyestrain or headaches. Check the alignment by focusing on a distant object, moving the binoculars away from your eyes while continuing to look through them. You should still be able to clearly see the images while the binoculars are held a foot or more away. Test the hinge that holds the two halves together to be sure you can easily adjust the size to fit your eyes.

Check the controls. To focus binoculars, you start with the main focus control, using your left eye. Then you fine-tune the focus with the diopter adjustment (usually found on the right lens) to bring the image for the right eye into focus.

You should be able to easily turn the central focus control with one finger while holding the binoculars up to your eyes. Watch out for controls that seem stiff, are too small to operate with ease, or are in a clumsy location. The same applies to the diopter-adjustment dial. (Look for a diopter dial with markings so you can quickly go back to your optimal setting after loaning someone else the binoculars.)

It pays to try out binoculars in the store; if you're buying online, check that the dealer offers full refunds.

Consider other features. Electronic circuitry gives some binoculars special capabilities. Binoculars with image stabilization use a battery-powered system you turn on and off to steady the image. (When you hold binoculars up to your eyes, even the slightest shakiness in your hands causes the image to jump. As a result, you see less detail in the image.) We tested two pairs, Canon 8x25 IS and Canon 10x30 IS. We found them to be effective and useful, as long as you don't mind the extra weight and size.

Attempts to combine binoculars and imaging are less successful, according to our tests. A few manufacturers have added digital cameras to their binoculars, including Bushnell and Simmons. While it might be tempting to think you can get great pictures of that tiny warbler you're seeing up close, don't be fooled. We found that the image quality of photos taken with those cameras is low, with sharpness and color poorly reproduced. And the picture is not necessarily magnified as much as the image you're seeing through the binoculars, since the camera uses a separate lens. Oddly, those models did not include tripod sockets, so it was difficult to shoot sharp images.