THE SOLUTION

You might think of fill flash when your main subject is in harsh midday light, but what you may not realize is that it can also be used to shed light on dark backgrounds. If your ambient light provides enough illumination to light your subject, you can add a fill flash to the background to match the light level on the subject. The key is to set the exposure for the subject based on available light, and then add the fill flash to the background to match the foreground exposure.

We’ve already learned about the differences between manual flash and TTL flash (see this page, as well as how to determine your appropriate flash-to-subject distance in manual and your flash range in TTL (see this page). Those same principles apply here, only your subject—the area you are lighting—is the background. So when establishing your flash-to-subject distance or flash range, just remember that your flash needs to be the correct distance from the background, rather than from the subject.

Also, depending on the color of the light falling on your scene, you may want to add a colored gel to your flash to warm up the light. If you do this, you will need to compensate for the loss of light caused by placing the gel over the flash head. An amber gel, for example, subtracts about 2/3 stop of light, so you’ll need to move your flash closer to the background to compensate. How much closer? Well, if your flash-to-subject distance calls for 10 feet, you would move the flash to about 8 feet. In the world of flash, one full stop means cutting your distance by 25%. Since this is only 2/3 stop, simply adjust accordingly.

With these settings in place, when you trip your shutter, the fill-flashed background should match the ambient-light exposure of the subject in the foreground.