Any photograph, whether taken with a film or digital camera, is created by focusing light through a lens onto a light-sensitive recording medium. In a film camera, the film negative serves as that medium; in a digital camera, it's the image sensor, which is an array of light-responsive computer chips.
Between the lens and the sensor are two barriers — the aperture and shutter — which work in concert to control how much light makes its way to the sensor of a digital camera. The actual design and arrangement of the aperture, shutter, and sensor vary depending on the camera, but Figure 7-1 offers an illustration of the basic concept.
The aperture and shutter, along with a third feature — ISO — determine exposure, which is basically the picture's overall brightness and contrast. This three-part exposure formula works as follows:
Aperture settings are stated as f-stop numbers, or simply f-stops, and are expressed with the letter f followed by a number: f/2, f/5.6, f/16, and so on. The lower the f-stop number, the larger the aperture, ...