Introducing the Exposure Trio: Aperture, Shutter Speed, and ISO

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.


Figure 7-1: Aperture size and shutter speed determine how much light strikes the image sensor.

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 (controls amount of light): The aperture is an adjustable hole in a diaphragm inside the lens. You change the aperture size to control the size of the light beam that can enter the camera.

    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, ...

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