Fill flash is a photographic technique used to brighten deep shadow areas, typically outdoors on sunny days, though the technique is useful any time the background is significantly brighter than the subject of the photograph, particularly in backlit subjects. To use fill flash, the aperture and shutter speed are adjusted to correctly expose the background, and the flash is fired to lighten the foreground. Most point and shoot cameras include a fill flash mode that forces the flash to fire, even in bright light. Depending on the distance to the subject, using the full power of the flash may greatly overexpose the subject especially at close range. Certain cameras allow the level of flash to be manually adjusted e.g. 1/3, 1/2, or 1/8 power, so that both the foreground and background are correctly exposed, or allow an automatic flash exposure compensation.
If you have a 35mm camera with a dedicated flash, just set it to TTL mode but you should experiment and adjust the amount of the fill flash to suit your taste. Most dedicated flash units have plus or minus settings or use the camera’s exposure compensation dial to control the amount of flash. Try different flash exposure compensation value sets. For example, start with -1/3 and move up to a full -1 stop. Take plenty of images until you find the right exposure. Find and use the Force Flash mode; every camera’s name for this setting will be different so check the manual. For staged photographs, mark where your subject should stand to ensure that you’re within range. Zoom in and out if you cannot stand near enough. Or, move closer in or farther out if you do not have a zoom lens.
Sunny days will create shadows on subjects. Set camera to manual mode. If not, your auto mode will believe that there is enough light, and this will create shadows or even turn your subjects into silhouettes. Set flash to medium, and take a shot. If this does not create enough light, set flash to high. Take one image at a time so that you do not waste your memory. For stronger flashes, use lower settings, or stand farther away. Use a medium fill flash setting on cloudy days. Natural colors will appear brighter.