Laura Erickson's For the Birds

Last time I talked about how the most important feature, when buying inexpensive binoculars, is getting a low magnification power—no more than 8x, and I mentioned that 6x is surprisingly effective.

Binoculars are always described with two numbers, such as 6x32. The second number is the size of the objective lens in millimeters. In inexpensive binoculars, that number should always be at least 5 times the first number so your image will be bright enough. Of course, the bigger that number is, the bigger, and heavier, your binoculars, so the optimal choices are 6x30, 7x35, 8x40, and 10x50. With the highest quality glasses, the kind you pay a king’s ransom to buy, the glass is ground so precisely, and has such sophisticated coatings, that you can afford to get smaller ones, like 10x40 or 8x32, but I wouldn’t try this with even mid-range binoculars, much less downright cheap ones.

There are two styles of binoculars—roof prisms and porroprisms. My first pair were porroprisms—those are the binoculars with the obvious bend in them, like the ones used in the little Pixar robot Wall-E’s eyes. Roof prisms have straight barrels. The advantage of porroprisms is that they have one fewer glass element, so provide both a brighter image and superior clarity for the same quality of glass. But because of the way they focus, they also are more likely to allow dust and dirt to work into the optics unless they have armored waterproofing.

At some point while I had my first pair of binoculars, I got a new pair of eyeglasses and suddenly everything in my view was bigger and clearer. I hadn’t realized that every pair of binoculars is designed with a feature called “eye relief,” the precise distance at which the optical lens should be held from your eyes. When you don’t wear glasses, the eyecups hold your binoculars the right distance from your eyes. My binoculars had a very short eye relief, and even though I kept the eyecups folded down, as everyone who wears glasses should do, my glasses held the binoculars too far from my eyes. My new, thinner pair of glasses made the image much larger and easier to keep in focus. If you’re buying binoculars for someone who wears eyeglasses, make sure the eye relief is big enough for those glasses—as much as 18 millimeters or more if the glasses have thick lenses or big frames. And if you wear eyeglasses, make sure you keep the binocular eyecups down to get the best view.

The other issue to consider in choosing binoculars is basic comfort. If they don’t fit in your hand nicely and have a comfortable neck strap, you’re not going to enjoy putting them on.

Following these principles, you can get fine binoculars for about $300, and a reasonably good pair for under $100. During tough economic times, it’s especially important to get the best value for your dollar, but I think even when money is more free-flowing, it’s easy to yearn for the very best when very good can do. Just remember that top line binoculars now cost over $1600, some over $2000. The difference between that and a good $300 pair of binoculars is the cost of a trip to a wonderful place to see some birds.