What are exit pupil, eye relief and eyebox?
A beam of light emerges from the rear of a riflescope. Its diameter is called the exit pupil. In a simple example, an effective objective diameter of 50 mm divided by ten-times magnification gives an exit pupil of approximately 5 mm. This value describes the beam, not directly how bright the image appears.
A beam of light emerges from the rear of a riflescope. Its diameter is called the exit pupil. In a simple example, an effective objective diameter of 50 mm divided by ten-times magnification gives an exit pupil of approximately 5 mm. This value describes the beam, not directly how bright the image appears.
Eye relief describes how far behind the last lens the intended viewing position lies. The eyebox, by contrast, is the three-dimensional area within which the eye still sees a largely complete image. Outside this area, dark edges or shadows can appear. A single eye-relief figure therefore does not fully describe the eyebox.
Your eye also plays a part. Its pupil gets larger or smaller depending on ambient light. If it is smaller than the emerging beam, it cannot receive all the light available. A larger exit pupil therefore does not make the image brighter in every situation. Glasses, eye position and optical design also influence the view.