brightness
Brightness is the ability of a telescope to gather and transmit enough light to form a bright, sharp image. The relative luminance value is the square of the exit pupil diameter. The brightness of the image is relatively high. However, this brightness value cannot completely increase the brightness of the light on the naked eye, because the light passing through the binoculars is 100% effective only when the exit pupil diameter is consistent with the pupil diameter of the eye.
