The f stop controls a len's diameter and therefore controls the amount of light hitting the camera sensor. Therefore the f stop controls exposure which is critical for good photographs. Note that the len's aperature is "inversely" proportional to the f stop because the len's radius is equal to the len's focal length divided by the f stop.
The f stop range is based on the amount of light that hits the camera sensor and is the square root of the area. Each f stop doubles the area exposed to light and therefore doubles the amount of light hitting the sensor.
| Aperture Area | f Stop |
|---|---|
| 1 | 1 |
| 2 | 1.4 |
| 4 | 2 |
| 8 | 2.8 |
| 16 | 4 |
| 32 | 5.6 |
| 64 | 8 |
| 128 | 11 |
| 256 | 16 |