8×40

The designation 8x40 commonly refers to a pair of binoculars with an 8x magnification and 40mm objective lens diameter. This configuration is a popular choice for general-purpose use, offering a balance between magnification and field of view. The 8x magnification allows the user to bring distant objects closer, making it suitable for activities such as birdwatching, wildlife observation, and general sightseeing. The 40mm objective lens diameter indicates the size of the front lenses, which gather light. A larger objective lens diameter generally allows for a brighter image, especially in low-light conditions, and can also contribute to a wider field of view.

The "exit pupil" of an 8x40 binocular is calculated by dividing the objective lens diameter by the magnification, resulting in approximately 5mm (40mm / 8x = 5mm). This size is considered good for daytime use and can perform reasonably well at dusk or dawn, as it is close to the typical size of the human pupil in bright and moderate light conditions. The field of view, which is the angular extent of the scene that can be seen through the binoculars, typically ranges from 6 to 8 degrees for 8x40 models, offering a decent sweep of the surrounding area. These binoculars are often relatively lightweight and compact, making them convenient to carry for extended periods.