Power ranges

On all binoculars, you’ll find two numbers with a cross between them: 8x30, 7x21, 8x40 are some examples. The first, lower number is the magnification, so an 8x pair will magnify eight times, or make things look eight times closer than without them.   

Don’t be fooled into thinking that the higher the number, the better the binoculars will be for birdwatching. You won’t be able to hold steady anything above 10x at the very most, and 7x or 8x are better, especially if it’s windy. And ignore all variable-power (zoom) binoculars. They don’t let enough light in for birdwatching. 

The second number - x30, x21 or x40 in our examples - is the width of the largest lens, called the objective lens, in millimetres. So an 8x30 magnifies eight times and has an objective lens 30 mm in diameter. The larger the objective lens, the more light the binoculars let in and, usually, the more of any scene you have in view. 

This means that an 8x30 is better in dull weather or at night than an 8x21, and it’s easier for finding and following individual birds. But it’s also heavier, so you have to choose between light gathering and ease of use and whether you will be prepared to carry them around all day.