Almost every digital camera is equipped with automatic flash. Most cameras have several flash settings for different lighting conditions. The flash can be set to automatically trigger when the light conditions are too dim, and there are usually several other settings for greater control over the flash.
The flash is usually integrated into the body of the camera. This is very convenient -- just shoot the camera and allow the flash to come on if it is needed. There are, however, a few problems related to the close proximity between flash and lens.
The most common problem is red eye. Everybody has seen this -- the eyes of people (and even animals) take on a weird red glow. This is caused by the light from the flash reflecting back from the retina of the eye. The thin red blood vessels in the retina cause the red colour.
Some cameras have a flash setting which reduce this red eye effect. This works by firing a short flash before the picture is taken which causes the iris of the eye to become smaller.
Another problem caused by integrated flash is a lack of depth. The reason for this is the even illumination over the entire surface of the subject. Shadows which normally give a sense of depth are eliminated.
Both red eye and flatness can be reduced with a separate flash unit. They can be powered with a 'hot shoe' (a bracket on the camera body) or a cable which synchronizes the flash with the built-in flash of the camera.
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By moving the source of the flash away from the lens, added depth is created and the subject's eyes are not directly illuminated. External flash units also give you more options for aiming the flash -- the light can be bounced off other objects for a more subtle effect.
Not all flashes are created equal. They are available in various strengths, and the power of the flash determines how much area it can light up. Most manufacturers specify the maximum range of a flash. This distance can be achieved when the aperture of the camera is fully opened.
Objects which are closer to the flash will appear brighter. This effect can be used for separating your subject from the background, but it can also create problems if you wish to capture several people or objects which are at various distances from the camera. The only solution to this is to pose your subjects so that they are all at the same distance from the flash.
Digital Photography
Besides auto mode and red eye reduction mode, most digital cameras have several other flash settings. Flash off mode can be used to override the flash completely, allowing you to compensate for low light by increasing the aperture opening. Fill flash mode is useful when there is a bright light source behind your subject which would otherwise cause the picture to be too dim. Slow sync mode causes the shutter of the camera to remain open longer than normal. This allows the camera to absorb the ambient light after the flash has fired to create a more natural effect.
Creative use of the flash settings can allow you to achieve special effects. For example, slow sync mode can be used to blur the background of a picture while keeping the subject sharply focused. This is achieved by moving the camera slightly after the flash has fired.
