Binoculars are a very handy devices and an indispensible piece of equipment for many activities such as bird watching, camping and astronomy. However, people using them do not always understand very much about them, so a little extra knowledge can increase your enjoyment of using binoculars.
In general terms, magnification refers to the viewing power of the binoculars. For example, a pair of 7×35 binoculars will let you view an image seven times larger than with the naked eye. Typically, the lower the power, the wider an area you can see and also, the brighter the image. This is most relevant when viewing at dawn or dusk. High-powered binoculars are most useful for viewing distant objects over open landscapes with plenty of light.
This refers to the measurement of the objective lens i.e. the furthest lens from your eye. The objective lens draws in surrounding light in a similar fashion to that of a camera lens. The size of the aperture in a pair of 7×35 binoculars is 35mm. larger apertures allow in more surrounding light, but at the expense of an increase in size and weight.
Poorly focused binoculars can help to cause eyestrain, dizziness and headaches. Make sure that your binoculars are calibrated correctly before and after use, especially if you are lending them to someone else to use.