On a recent trip to Yellowstone with a group of bear scientists, our caravan would screech to a halt and all would pile out. Telescopes would be set up on tripods and binoculars uncapped to try and see what our guide spied, sometimes miles off on a mountainside. His eyesight was legendary. One grizzly, a large male on top of a ridge, could not be seen by most of the group with the naked eye. Those of us with our own binoculars realized the inadequcy of our glasses brought from home. They may have worked great at the opera or concert, but my little compact binoculars were woefully inadequate to see a grizzly bear a mile up a mountain.
Binoculars come in all shapes and sizes. But what did those funny numbers mean? Is an 8x30 better than a 12x50? The answer depends upon what you are using it for.
There are several things you need to know about binoculars before you consider which kind you should buy. Things like power, focus, a diopter or not, the physical size and the objective lens size are critical in the selection process.
You'll notice most binoculars have two numbers. The first number is the power. For instance a 10x50 binocular will have a power of 10. This represents the factor by which things will be magnified. An 8x40 will magnify a bird eight times. You can get power ranges between 4 and 25. For bird watching, you might want to look at a low power binocular in tight brush conditions, whereas if you want to use your binoculars for astronomy, you might want to consider a 25 power. The larger the magnification, however, the harder it becomes to hold the binoculars steady, unless you have a tripod, monopod or tree to balance it on. For wildlife watching, hunting and NASCAR racing, you might want a range between eight to 12. A higher power may seem like the macho thing to go for, but when you are looking through your binoculars with a high power set, the field of view may be smaller, making it more difficult to find what you are looking for. There are zoom binoculars that allow one to adjust the power, but critics say they rarely offer good quality views.
Some binoculars, usually on the cheaper scale, are permanently focused, which isn't necessarily a bad thing. Others have a center rocker-arm focus, a dial in-between the lenses which allow the user to adjust the focus. A third type is the barrel focus, where one twists a knob. When speed may be a factor, as in birding or hunting, the barrel focus will be slow. Choose for speed.
A diopter is a focus adjustment, usually on the right eyepiece. Because people rarely have both eyes exactly the same, this allows the user to individually adjust focus to match your eyes.
A pair of binoculars might be attractive if they can fit in your shirt pocket but they might not be so great for distance or field of view. On the other hand, a huge set of binoculars might impress your buddies, but your arms will complain later. For the same power and objective lens, you generally will pay more for smaller, lighter binoculars.
It is very important to know the second number in a pair of binoculars, this represents the size of the lens and how much light it will let in. The greater the ratio between the two numbers the sharper your image typically will be. If you're going for a set of NASCAR glasses, you don't necessarily need a lot of light since racetracks are lit pretty well. On the other hand, for astronomy, you'll want as much light as you can get. You might find that viewing through an 8x40 you will see better than through a 10x36. Generally, if you had to choose between power and objective lens, go with the latter.
New stabilizer binoculars are really groovy, especially if you have a natural tremor in your hands. Battery powered and often with a little computer inside, these types of binoculars stablize the image in view. Oftentimes they have all kinds of additional features as well. They're a little bulkier, but you'll find the stability is just what you need after a hard night of drinking.