Flash Techniques.


We all know how to use a flash right? Either you pop up the flash when you need extra light, or perhaps your camera in automode does this automatically. But there is a lot more to using a flash than this simple method. Of course, using a flash is highly dependant on your camera, but many cameras have advanced flash capability that you can use to take better photos.

Daylight Fill Flash: The conventional wisdom is that you should never take a photo with the sun and your subject in front of you. However, dramatic scenes, such capturing a person with the setting sun in the background can be very rewarding. Unfortunately, you cannot simply pick up your camera and photograph such a scene. This is because there is too much contrast in the scene, and the camera cannot faithfully reproduce the bright light of the sun, and the shadows (person's face, etc) cast by the sun.

Face is underexposed because the camera metered the sky behind the subject for proper exposure.

Metering on the face results in a properly exposed face, but over-exposed sky.

In the above photos, the camera usually exposes on the bright background, which makes the foreground in the shadows too dark. Or if you expose for the foreground, the background becomes too bright. This is because there is not enough dynamic range (ability to capture both light and dark areas) in a camera. Thing is, a camera cannot "see" as good as the human eye, so this is the result.

When these situations are unavoidable, fill flash can sometimes be used - provided your subject is within range. Generally any camera can be used with this method, as the camera and flash simply expose for the proper photo. The reason this works is the flash has a limited range, so it cannot affect the background. Simply put, the camera exposes for the background and the flash exposes for the foreground. The result is that the light reaching the subject in the foreground (from the flash) is relatively equal to the light coming from the sun. So in a sense, you are augmenting the sun with the flash, balancing the light that is cast onto the scene.

Back-lighted photo.

Using fill flash to correct foreground shadows.

So, how do you setup your camera to use fill-flash. In the example above, using a Nikon Coolpix P330 compact camera, I first took a photo using Aperture Priority to obtain a proper exposure (you could use most exposure modes to do this). If your camera only has auto exposure, then use that mode - any mode that will result in a proper exposure of the scene will work.

Then I simply raised the flash and retook the photo. Note though, some cameras - when in Auto mode, will not fire the flash; other cameras have Auto mode, Auto + Flash mode, and so on. You'll have to determine which mode on your camera will allow the flash to fire.

To be successful, all you need is for your camera to properly expose the scene, lift the flash, then take the photo. The reason this works is that the flash has a limited distance of a few feet, so it ends up only affecting the foreground - not the background.

Some dedicated flash units, such as Nikon's SB700, SB900, and SB910 have a TTL-BL mode (TTL-Balanced) wherein the flash is smart enough to balance with the background. This can be an alternate method for obtaining such results.

I might point out that in this example, if I underexposed the background a bit in the first step, I could have likely obtained a very dramatic sunset.

Using Fill Flash to "Assemble" a photo

More complex Fill flash is typically used in daylight conditions when "help" is needed for balancing the contrast. This typically requires an external flash, or at least a camera that can set the flash exposure compensation independantly from the cameras exposure.

This photo was metered for the interior area of the bridge, which resulted in over-exppsure of the outside.

This photo had it's exposure set for the outside, which resulted in under-exposing the interior.

In this scenario, neither photo is correct, although in each case, the camera did meter the designated point correctly. The problem is that cameras just do not have enough dynamic range to capture the entire range of light values.

This technique is similar to the fill flash technique above, but the complexity requires putting both camera and flash into manual exposure mode. The camera is metered for proper exposure of the outside part of the scene, and the flash is metered for proper exposure of the interior. Since the flash has a limited distance of only a few feet, it will not interfere with the distant exterior exposure. The result is in a properly exposed photo. In a sense, the flash "filled in" the interior; hence the term "fill flash".

In essence, you set exposure on the camera for the background, and you set exposure on the flash for the foreground. (Note: depending on your camera and flash, you may not need to go into manual mode. Experimentation is the key). Again, this is similar to the first fill flash example, except more critical exposure settings may be required. And the problem here is simply lack of dynamic range on the part of the camera, and not because of the sun's orientation.

Rear Curtain Sync.

To understand rear-curtain sync, it is helpful to compare it to how the standard flash works. In the diagram below, in the standard flash scenario, the shutter opens, the flash fires, and the shutter closes. The shutter speed in such an operation is typically 1/60th of a second. The background is not exposed, as 1/60th of a second is not enough time to properly expose the background.

In rear curtain sync, the shutter speed is typically much longer - long enough to expose the background. Then, and only after the background is exposed, the flash fires and the shutter closes. The leading edge of the shutter is typically called the "front curtain" and the trailing edge of the shutter (when the shutter closes) is called rear curtain.

The terms front and rear curtain come from mechanical shutters wherein the shutter opens with one curtain, and the shutter closes with a second curtain. Since the flash fires when the shutter (or rear curtain) closes, it is typically called rear-curtain sync.

It is important to note that in rear-curtain sync, any movement that occurs in the scene while the shutter is open (before the flash fires), will be recorded in the photo.

Using a flash in low light conditions.

Using rear-curtain flash.

In the above photo to the left, standard flash settings were used - i.e. the shutter is open for 1/60th sec, and the flash fires when the shutter opens. For that reason, the foreground is illuminated by the shutter, but the background is dark as 1/60th sec is not long enough to properly expose it.

In the right photo, rear curtain sync was used, with the shutter set for 1/2 sec. The shutter was open long enough to obtain proper exposure of the background, and when the flash fired as the shutter was closing, properly exposed the foreground. Some experimentation of shutter speeds is in order to obtain the proper balance. And it should be stated that a tripod is necessary for such slow shutter speeds.

Summary: You have been given several different methods of using a flash for creative exposure, or when your camera is tricked into mis-behaving. Your capability will be highly dependand on the your camera and flash'es capabilities and adjustments. However, in these examples, I used a Nikon Coolpix P330 compact camera for the daylight fill flash and the rear-curtain sync examples. In the assemble a photo example, I used a Nikon D90 DSLR with SB700 Speedlight. Since I was able to obtain good results by just using a compact camera, don't feel you need the most expensive equipment to learn these techniques.