These days, binoculars come with many bells and whistles such as waterproofing, stabilization, coating and automatic focusing. Before thinking about all the specification you would like your binoculars to have, you need to decide what you are going to use them for.
Binoculars are classified by two numbers (ex: 8x40 or 7x35.) These numbers tell you two things:
The first number will tell you the magnification or how many times an image will be enlarged in the view finder. When looking at a bird through a binocular of 8x40, a bird will look 8 TIMES bigger than just using a human eye.
The second number signifies the diameter of the front lens in millimeters. The bigger diameter of the front lens, the brighter and sharper image you will see in your binoculars. Think about these two numbers when deciding what binoculars to buy for your given usage. The diameter of any given binoculars relates directly to how big it is. Keep this in mind as to how portable you want your binoculars to be.
The following are popular uses for binoculars and their most common rating:
Hunting/Birding: 8x40, 8x42, 10x40 or 10x42
Sports: 6x30 or 8x40
Astronomy (hand held): 7x50 or 10x50
Astronomy (tripod): 10x70, 20x80 or 25x100
Hiking: 8x25 or 10x25