Binoculars are usually described by two numbers such as 10×50 or 8×30. If we take 10×50 for example, the first number is the magnification or power of the binoculars. It states that the image you are viewing through the binoculars is ten times larger than it actually is. The second number, (50) gives us the diameter in millimetres of the front or objective lens. A further number printed on binoculars is the ‘field of view’. This gives the width of the area being viewed at a stated distance.
The most popular and commonly used binoculars have a magnification range of between x7 and x10. These are generally best for close to mid distance use such as bird watching, horse racing, and viewing objects quickly without having to spend time setting up a tripod. The higher powered models help to see more detail, but when hand held, magnify any movement of the hands, resulting in a shaky image. Holding the binoculars steady is far more difficult with anything greater than a magnification of x10. One way around this is to support the instrument against a wall or tree whilst viewing, although there are limitations with regards to comfort and watching a moving object such as a bird.
Another problem with higher magnification is that the field of view is smaller, so locating an object and keeping it in view can be a difficult task. Anything more than a x10 magnification normally requires a tripod, and for x15 or greater it is essential.