Most cameras with built-in flashguns have several modes, different ways that the flash can be used. Knowing the best mode to use under different circumstances is very important for good flash photography.
The most commonly used flash mode, this is the default flash setting on most compact cameras. If the cameraâ€™s light metering system detects that the light levels are too low for a steady hand-held shot, it will automatically activate the flash.
Unfortunately nobody seems to have yet thought of the idea of linking this to the autofocus system, so the camera doesnâ€™t know if the subject is out of range of the flash. Auto flash is fine in most normal circumstances where the subject is not more than a couple of metres away, but if the subject is further away then itâ€™s best to turn the flash off and rest the camera on a solid surface to avoid shake.
One of the most common problems with close-range flash photos is â€œred-eyeâ€, where the subjectâ€™s eyes appear to be glowing a rather demonic red. Most flash photographs are taken in low light conditions, and in the dark the iris of the human eye opens up wider to take in more light. Unfortunately this means that the light from the flash, which on most compact cameras is very close to the lens, enters through the wide-open iris and reflects off the blood vessels at the back of the eye.
Most cameras have a flash setting that reduces this effect by firing a short burst of flashes before the picture is taken. The subjectâ€™s eyes react to this light by contracting the iris, reducing the amount of flash light that can enter. It doesnâ€™t always completely eliminate red-eye, but it does usually make it less noticeable.
Many photo-editing computer programs have the ability to automatically detect and remove red-eye in portrait shots. Some cameras also have this ability built in, so red-eye can be removed after the shot has been taken.
Night portrait/slow sync
Most cameras have the ability to use the flash in conjunction with a slow shutter speed. The correct term for this is slow sync flash, but it is often referred to as night portrait mode, since this is the use to which it is most frequently put. When using this mode for portrait shots it is important to keep the camera steady, preferably with a tripod, and for your subject to keep as still as possible. The cameraâ€™s metering system will set a slow shutter speed that will correctly expose a dark background, but will also fire a fill-in flash at the end of the exposure to illuminate the foreground. Some cameras also include a slow sync mode with the anti-red-eye pre-flash function.
Pretty simple, but very useful, this turns the flash off. Use this mode if your subject is out of flash range, but remember to keep your camera steady and tell your subject not to move, because it will usually result in a long exposure.