Riflescopes Explained : Exit Pupil
The small circle of light that appears in the eyepiece when you hold a scope at arms length is called an exit pupil. A formula for exit pupil is as follows: Divide the objective lens size in millimeters by the magnification.
Example:
| 3-9X40 scope is set at 3X, 40 divided by 3 equals 13.3 mm |
- | which is large enough for almost all low light applications. |
| 3-9X40 scope is set at 9X, 40 divided by 9 equals 4.4mm |
- | The difference in available light from the larger exit pupil is significant |