The best binoculars for birdwatching are 7x35 or 8x42—the first number is the magnification and the second is the diameter of the front lens in millimeters, which controls how much light the lens lets in. Higher numbers like 10x50 mean higher magnification and more light, but they're heavier and they magnify movement, so they're better to use with a tripod. On the other hand, magnifications like 8x20 are lightweight and easy to carry, but they have a smaller field of view and let in the least light.