People often get confused by the two numbers that describe binoculars, but they actually have a simple explanation. Memorising this simple formula will make shopping for new optics much easier.
First Number (Magnification)
The first number in a binocular description is the magnification. In this case, the magnification is 10 power, written as 10x, which means the image appears 10 times closer than when viewed with the naked eye.
Second Number (Objective Lens)
The second number is the size of the objective lens, written in millimetres. The objective lens is the larger lens, the one farthest from your eyes. The objective lenses in 10x50 binoculars are 50mm in diameter.
The higher the magnification, the closer the image appears. The price also goes up. Larger objective lenses gather more light, so they are helpful when viewing images in lowlight conditions when animals are often most active. Larger objective lenses add size and weight and increase the price of the optics.