A beginner's guide to binoculars

The one piece of equipment that is absolutely indispensable to a birdwatcher is a good pair of binoculars. I can say this from experience. The first year of my birding career was spent without binoculars and without a bird book. I used to stalk birds and take careful notes, then go to the county library to look up the birds in their ancient copy of Peterson. I learned a lot that way, but when I graduated from high school my parents gave me a pair of binoculars and my birding mentor gave me my own copy of Peterson and it changed my whole life.

Buying a pair of binoculars There are lots of reviews of binoculars on the web. In addition, Birding magazine runs reviews about once a year. My rule of thumb is very simple:

Buy the most expensive pair of binoculars you can afford.
Do not go cheap.

The reason is also simple. The cheaper binoculars have surprisingly good optics. Modern computers have taken a lot of the artistry out of optical design and manufacturing. However, the structural robustness of a pair of binoculars is another matter. Many cheaper optics are designed for a life cycle that does not at all reflect the usage that an active birder will put on his binoculars. Virtually any binoculars offered by discount houses or sporting goods houses are designed for the casual user. They are made for people who will use them at horse races and football games, perhaps 10-20 hours per year under benign conditions. An active birder will put a lifetime of use on this sort of optics in about a year. After that time, things will start to go wrong and most of them will be irreparable.

I went through about six pairs of progressively more expensive binoculars while learning this lesson. I pass it on to you for free.

In my experience, the threshold of utility for a pair of binoculars is about $350 (in 2006 dollars). At this level, one begins to encounter binoculars with very nice optics and reasonably sturdy construction made by reputable firms with reasonable warranties and effective support capability. If something goes wrong, you can get it fixed. There are nevertheless two points that you will want to satisfy yourself on which vary widely among optics at this level. These are eye relief and close focusing.

Eye relief is important for eyeglass wearers, who need long eye relief (big number) because they are essentially holding the binoculars further away from their eyes. If you wear eyeglasses, don't try to use the binoculars without them. It just gets to be too much of a hassle. I know because I resisted it for years after age drove me to reading glasses. It doesn't take much effort to learn to use eyeglasses and binoculars together. You should do it.

Close focusing is pretty much self-explanatory. If you are lucky enough (or skillful enough) to get into close quarters with a small bird, you want to be able to take maximum advantage of the experience. It doesn't seem like much, but having to take a step or two back from a good bird is really galling. I would like to be able to focus on my toes. Unfortunately, my Leicas won't do that, but that is what I would like.

When you get up to the $1000 level, the optics are so superb that I cannot distinguish any differnece among them. At this level, any binocular will give you light, bright, colorful images that snap into focus. And those superb optics come in a chassis you can practically drive nails with. At this level, you can confidently expect that your binoculars will outlive you. If you can stretch your budget to one of these wonderful instruments, do it. The only criterion you need consider is personal comfort. Pick the one that feels best to you, sits in your hands nicely, comes readily to your eyes, and complements your personal style.

How much power? Binocular manufacturers use two numbers to characterize their models. The first one is the power. This is the amount of magnification. This is a linear scale: a binocular with twice the power makes the image look twice as big. The other number in the specification is the diameter of the objective lens (the one closest to the bird). Thus a 10 x 42 binocular is ten power with a 42 mm objective lens. The significance of the objective lens is its light-gathering power. A bigger objective gathers more light and generally gives a brighter, more pleasing image. Note that the ability to gather light is a function of the area of the lens, and is thus proportional to the square of the diameter of the lens. Simply put, a lens with twice as big a diameter with gather four times as much light. So even a small difference in the size of the objective is significant.

There are two basic designs of binoculars, porro prism and roof prism. Porro prism binoculars are the kind that you see submarine skippers using in old WWII movies. Roof prism binoculars look like two telescopes lashed together. Today, there is little point in going for porro prism binoculars. The roof prism design contains fewer elements, has fewer internal reflections (where light is lost), and weighs less.

The old rule of thumb for porro prism binoculars was that the objective diameter should be five times the power. Thus, the popular sizes were 6 x 30, 7 x 35, and 8 x 40. There were some 10 x 50s around, but they were so heavy that few could hold them steady. Roof prism designs are more efficient, so you can combine higher power with a smaller objective and still get superior image quality. The two dominant design points these days are 8 x 42 and 10 x 42. It sounds contradictory, but it's not, really. Both designs have strengths that play to different types of birding.

The 8 x 42s are lighter, easier to point, and have a very bright image. They come into their own in close quarters, under closed canopies, or when chasing small agile birds. The 10 x 42s are preferred by birders who are particularly interested in waterfowl, shorebirds, gulls and terns, hawks, seabirds, and birds of the open spaces: savannahs, grasslands, deserts and salt marshes. In these environments, the narrower field of view is not a problem and the ambient light levels are usually high enough to give a plenty bright picture.

So it comes down to a matter of what kind of birding you do and how much you can spend. Isn't that true of life in general?