essential skills: photographic lighting
Intensity and duration Intensity Light intensity is controlled by the aperture in the lens. Actual aperture is the size of the diameter of the iris built in to the camera lens. The aperture is a mechanical copy of the iris existing in the human eye. The human iris opens up in dim light and closes down in bright light to control the amount of light reaching the retina. The aperture of the camera lens must also be opened and closed in different brightness levels to control the amount or intensity of light. The right amount of light is required for correct exposure. Too much light and the lightsensitive medium will be overexposed, not enough light and it will be underexposed. As the aperture on the lens is opened or closed a series of clicks can be felt. These clicks are called f-stops and are numbered. When the value of the f-stop decreases by one stop exactly twice as much light reaches the image plane as the previous number. When the value of the f-stop increases by one stop half as much light reaches the image plane as the previous number. The only confusing part is that maximum aperture is the f-stop with the smallest value and minimum aperture is the f-stop with the largest value. The larger the f-stop the smaller the aperture. Easy!
f16
f8
f4
Activity 1 Carefully remove the lens from either a small-format or medium-format camera. Hold the lens in front of a diffuse light source of low intensity. Whilst looking through the lens notice how the size of the aperture changes as you alter the f-stop. Record and discuss the relationship between the size of the aperture and the corresponding f-stop number displayed on the barrel of the lens or in the LCD panel.
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