How does power affect field of view or brightness?
A high power number usually means a smaller field of view and lower brilliance of the image that reaches the eye. Binocular brightness is critical for indoor sports, outdoor birding in shaded areas and hunting. All binoculars can be used at night or during the daytime. But certain binoculars are better adapted to night viewing than others; some even have “night vision” modes. Binoculars with the largest objective lenses are desired because more light can be admitted. The average diameter of a person’s eye during the daytime under average conditions is about 4 millimeters but at night expands to about 7 millimeters. Therefore, a binocular that utilizes the full diameter of the expanded pupil is better for night use. Thus, a 7x5O which has a large exit pupil (7 mm) and utilizes the full diameter of the expanded pupil of the eye is considered to be an especially fine night binocular.
