Using Your Flash
As previously mentioned, a good accessory flash unit can be used in a variety of different ways. It can improve lighting conditions in virtually every situation and allow you to create some special effects as well.
This technique adds light to shadows to create better balanced exposures. It also throws light onto the foreground of backlit areas to keep images from appearing as silhouettes. The secret to good fill-flash photography is to balance the light from the flash with the existing or ambient light. The ideal fill-flash setting will provide just enough light to bring the shadows within one or two stops of the highlights. Good flash and camera systems will automatically do this, or you can do it yourself.
You can use fill-flash techniques in a couple of different ways to augment or correct existing light. The following sections provide some tips on how to do so.
Bright Days
You're taking a picture of some kids at a school picnic. The sun is directly overhead, lighting up the tops of their heads and casting unflattering shadows under their eyebrows, cheeks, and noses. Set the camera to expose the sunlit faces correctly, and set the flash to go off about one or two stops less than the ambient light. This technique fills in the shadows but isn't the main light source. Similarly, when shooting digitally, expose for the faces correctly and compensate for the shadows in the image and contrast controls.
Backlighting
You're taking a picture of your aunt and cousin while they're visiting San Francisco. The Golden Gate Bridge is sunlit in the background, and your relatives are in a shady spot. Set your camera to expose properly for the bridge, and the flash to expose properly for them. You may want to bracket your exposures by slowing the shutter down one stop to make the background brighter, and then, if you can, bumping it up to a faster setting to darken the scenery. Changing the shutter speed won't change the lighting on your relatives because they're only being lit by the flash. In this case, the flash fills in the entire subject but is equal to the ambient light. Because the subjects would otherwise be in shadow, the flash is the main light for the subject.
Indoors with Good Lighting
You're at an evening wedding reception in a hotel ballroom. The bride and groom stop to visit at your table, and you want to take their picture. The room is comfortably lit, but not bright. You're shooting ISO 400 film, or in digital shooting have set your ISO at 400, if possible. You want the shutter to stay open long enough to capture some of the warm ambient light in the room. Choose a large f-stop, say f/2.8 or f/4, match the flash to the f-stop (which an automatic camera will do), and make sure the shutter stays open for 1/15th or 1/30th of a second. The room will not come out bright, but will look warm and friendly. The happy couple will be properly exposed by the flash and not blurred despite the long shutter speed. The reason is that most of their image was put on the film by flash illumination, which will be much brighter than the ambient light.
You can use an accessory flash or a built-in flash for fill-flash pictures. Check your camera manual for information on how to adjust exposures when using built-in flash.
Accessory flashes are adjustable, which means you can change the direction of the flash by tilting or rotating the flash head.
Bounce flash eliminates the flat, contrasting deer-in-the-headlights look that direct flash so often delivers. You'll still get good illumination, but the light will be indirect and softer, which makes for much more pleasing pictures.
To set up a picture with bounce flash, rotate the flash head toward the ceiling or to the side so it faces a wall. Low ceilings or walls that are close to your subject work best for this. If either is too far away, the bounced light might not be strong enough to provide adequate illumination. Using bounced light always requires that you increase exposures by several stops, since some of the light is absorbed or scattered when it hits the other surfaces. If this is the case, you'll need to use a wider aperture or faster film. If you have a connecting cord, you can take your flash off the hot shoe and move it closer to the reflective surface.
It's important to aim bounce flash correctly so the light falls on your subject, not behind it. If you aim the flash at the ceiling directly above your subject when taking a portrait, you might create “raccoon” shadows under your subject's eyebrows.
You can use multiple flashes to light a picture. A photo slave, which costs as little as $20–$30, senses another flash firing and instantaneously triggers the flash it's plugged into. If you have a flash meter, you can measure the output. Or, if you use a second flash that has its own sensor, you can aim that second flash at the subject from just about any position that lights up the subject well. Set the off-camera flash at f/8 or f/5.6, and set your on-camera flash at one to two stops less.
A photo slave will fire every time it senses a flash going off, so if your camera uses a flash burst to reduce red-eye, the slave flash will also go off too soon. If you're not the only one in the room with a flash, it will fire whenever anyone else takes a flash picture.
