The objective lens is the lens positioned furthest from the eye in optical devices such as binoculars, telescopes, and microscopes. In binocular specifications, it is represented by the second number and indicates the diameter of the lens in millimetres. For example, a 10x50 pair of binoculars has 10x magnification and a 50mm objective lens.
In photography and optics, the size of the objective lens plays a key role in determining how much light the system can gather, directly affecting image brightness and clarity. Larger objective lenses generally provide brighter images, especially in low-light conditions, making them important for wildlife observation, sports viewing, and long-distance photography.