What is exit pupil?
A6. The exit pupil in a binocular is the actual width of the beam of light that leaves the eyepieces and is measured in millimeters. You can see the exit pupil by holding the binocular up to eye level at arm’s length. The circle of light in each eyepiece is the exit pupil. To calculate the size of the exit pupil, divide the magnification power into the objective diameter size. A 10×50, 7×35, and 8×40 each have an exit pupil of 5. Higher magnifications generally lead to lower exit pupil.
The exit pupil is the round image one sees when looking through the eyepiece of the binocular, and is the image that actually reaches your eyes after being magnified and inverted. The exit pupil is a direct mathematical function derived from the size of the objective lens divided by the magnification. Therefore, a 10 X 50 pair of binoculars would have an exit pupil of 5mm. The larger the exit pupil, the more looking through your binoculars will mimic your natural vision. However, exit pupils of more than 7mm will serve little purpose, because the human eye can only dilate to an approximate maximum of 7mm.
The exit pupil refers to the size of the shaft of light transmitted to the eye. The larger the exit pupil, the brighter the image will appear. The exit pupil is an important indicator of the binocular’s low light performance. You can actually see the exit pupil by holding the eyepiece of the binocular approximately 12 inches from your eye. It is the bright circle of light in the center of the eyepiece. Exit pupil is expressed in millimeters and is normally derived by dividing the power into the objective lens diameter. A 7×35 binocular has an exit pupil of 5mm (35/7). A 15-power binocular with a 60mm objective lens diameter has an exit pupil of 4mm.
