When you're photographing in the bright sunlight of daytime, it might not ever cross your mind to pull out your flash and put it to use. But it's actually a great idea. When photographing in sunlight your camera will have a hard time keeping detail in the shadows, which typically go black.

Using a flash for a little bit of fill light will help even out the extremes in the tonal latitude in your image. Fill flash is especially useful when photographing people as shadows tend to form on faces in sunlight, especially during in the midday hours. Proper fill flash will eliminate those shadows.

Settings

I've said this so often now, but you really need the most powerful flash you can afford. Because using a flash in broad daylight requires a lot of power. Your flash exposure is strictly dictated by the aperture you're able to use at your camera's flash sync shutter-speed. Since this setting is often 1/250th of a second at the highest, you're going to find yourself stuck using a small aperture like f11 if you're working in sunlight. It takes a lot of light to illuminate a subject at f11, especially further than five feet. So invest in a powerful flash. The more light you can throw out into the scene, the better.

When you initially start using fill flash, you'll want to run some tests. Hopefully your camera and/or flash has the ability to adjust the flash exposure level. That setting is similar to exposure compensation on your camera, but only applies to the flash. So you can set the flash to expose at two stops under, but your ambient light exposure will remain normal.

If you can adjust your flash's exposure level, shoot a series of fill flash test frames with your flash at +1/2 stop, normal, -1/2 stop, and -1 stop. You'll get a good idea of what looks best. Most professionals would say to shoot with your flash set to underexpose by about one stop. This helps to keep the flash from overpowering the natural look of the ambient light. The idea is you want the flash to help fill in the shadows, but not overpower the ambient light.

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Another advantage to fill flash photography is that you'll get beautiful highlight reflections from the flash in a subject's eyes, which can bring life to a person's face. These tiny highlights add a nice accent to any portrait.

Another option to fill flash is to use a diffuser on your flash to help soften shadows. The major drawback to diffusers for fill flash is that they weaken the power of your flash. Most diffusers reduce the power of a flash by at least one stop, which can really hurt in a daylight fill flash situation. Depending on how much light you prefer for your fill flash work, you might find the diffuser works great.