While they may all look the same to novices, binoculars come with a good amount of variety. In a general sense, there are two main types of binoculars: roof prism and porro prism. Roof-prism binoculars (shaped like an H) weigh less and are more compact (and comfortable to hold) than porro-prism binoculars. These H-shaped binoculars are usually dustproof, waterproof and fogproof. (Fogproofing makes the binoculars usable even in very cold or humid weather, when most binoculars would fog internally.) In the past, porro-prism binoculars, which are shaped like a W, were considered optically superior to roof-prism models, but that is no longer the case. Technology has advanced so far that the sources we consulted said there is little optical difference between the two types of binoculars. However, porro-prism binoculars are cheaper to make, so they're a good choice if you are shopping on a budget. Porro-prism binoculars are not waterproof or fogproof.
When shopping for binoculars, the magnification and aperture numbers tell you how much detail you'll be able to see and roughly how large the binoculars will be. For binoculars described as 8x42, for example, the 8 is the magnification (or power). This means the binoculars make an object look eight times closer than the naked eye. The number 42 means that the lens farthest from your eyes -- called the objective lens (also called aperture or front end) -- is 42 mm. The size of the objective lens determines the bulkiness of the binoculars. A larger objective lens lets in more light, so binoculars with larger objective lenses are theoretically better in low light, but they are also larger and heavier than binoculars with a smaller lens.
Compact binoculars (which are handy for sporting events, concerts, hiking or general use) have objective lenses of 30 mm or smaller. They're lightweight and convenient, but usually provide less detail and brightness. Mid-size binoculars, with objective lenses of 32 mm to 35 mm, are often more comfortable to hold than full-size binoculars, but offer a dimmer view. Full-size binoculars, with objective lenses from 36 mm to 50 mm, usually offer the brightest image. You'll see some giant binoculars that are even larger. These are often used for stargazing (though 10x50 is also a good size for astronomy binoculars) and are best used with a tripod.
For general use, experts usually recommend 8x42 or 10x42 binoculars, especially if you don't want to pay more than $500. You can see more detail with 10x magnification, but unfortunately, any flaws in the optics or design of the binoculars are also magnified. For bird-watchers, experts recommend binoculars with 8x magnification because their wide field of view makes it easier to get the targets in view but they're not as heavy as 10x binoculars. Field of view is a measurement (in feet) of the diameter of the image you'll see 1,000 feet away. A wider field of view means you'll see more of a landscape or sports field without shifting your gaze.
The best binoculars have fully multi-coated lenses. This means that each internal lens has more than one layer of antireflective coating on both sides of all the lenses. Less desirable multi-coated lenses have coatings on only some sides (fully coated lenses are even less desirable). These lens coatings are designed to let more light through the binocular for a brighter image, as well as to correct for color distortions.
In addition, experts say you should look for the following when buying binoculars: