The first maneuver is to focus the glasses. If you have chosen seven-power binoculars, pick out a sign with lettering about 60 feet away (the distance should be about 10 times your height). Put the glasses to your eyes and, keeping both eyes open, place a hand over the end of the right barrel. Move the center-focusing dial until the image is clear. Then put a hand over the left barrel and turn the individual-focusing dial on the right eyepiece until the image is sharp. Now both eyes should be properly focused. With premium binoculars—$300 Leitz and Zeiss models—amazing precision can be achieved. The man with 20/80 vision can twist the dials and get the same prescription that he does from his optician for eyeglasses.
Once the glasses are focused, comparisons can be made between quality and cheaper models. The less expensive the glass the more indefinition there is around the perimeter of your view. There will be color fringes on the edges of the circle. Look at a square sign. Do the edges remain straight or do they bulge or appear to cave in? Look through the binoculars at the surface of a distant table or counter. Is it well defined or does the tabletop appear to buckle? Aberrations are common in poorly constructed binoculars. And always examine the glasses for scratched lenses or nicked frames. It is foolish to buy a pair that has been mishandled. The lenses, though set in cement, will shift if knocked about.
No pair is worthwhile unless it has prisms. These are apparent if you hold the binoculars about a foot and a half from the eyes. In the eyepieces you will see a round circle of light or a circle in a dim square in less expensive models.
Coated lenses are advisable. Inside a pair of binoculars there are more than a dozen surfaces that should be treated. To test for this, hold the binoculars backward, with the eyepieces toward a light. Look through the big lenses—called the objectives—and move the glasses slowly back and forth. If you see something inside that looks like a line of distant auto lights, the lenses have not been sufficiently coated.
These are simple, practical tests to make before purchasing. But there are other considerations, too. A man with large hands obviously will be uncomfortable with binoculars that are too small. The eyeglass wearer will get a better view using models with adjustable eyecups. Perhaps the buyer wants style—the latest rage is the long, thin-barreled model. The trophy hunter may prefer wide-angle binoculars, which are fine for scanning a mountainside, but they are hardly what a birdwatcher needs. Zoom glasses are not recommended, though they are advertised as five different binoculars in one. The zooms often go out of focus, and until they are perfected and operate with the precision of camera-zoom lenses they are not a good buy.
As to price, below $40 you pay your money and you take your chances. In the $50 to $70 range you can get very serviceable glasses among name brands, such as Nikon and Bushnell. But if you want the best, figure on $200 and up.
And be sure to remember, there is more to selecting binoculars than meets the casual eye.