What is indicated by the "10/42" specification on binoculars?

The "10/42" specification on binoculars indicates that the binoculars have a magnification of 10x and an objective lens diameter of 42mm. In this context, the first number represents the magnification level, meaning that the object being viewed will appear ten times closer than it would to the naked eye. The second number refers to the size of the objective lens, which is responsible for gathering light and ultimately determining the brightness of the image seen through the binoculars. A larger objective lens allows more light to enter, making the view brighter, particularly in low-light conditions.

This configuration is commonly used in binoculars to ensure a good balance between magnification and light-gathering ability, making them suitable for various applications such as birdwatching, sports events, or general use. Understanding this specification helps users select binoculars that meet their specific viewing needs.