Controlling Flash Exposure
When using the built-in or external flash, there are times when the main subject is too dark or light. This happens if the subject is too close or too far away, too small or off center, or is against a very dark or light background. At other times, you may be using the flash for fill lighting and want to control how bright it is. As you've seen , you can use exposure compensation, exposure bracketing, and exposure lock to control camera exposures. With some cameras, you can have the same control when using flash.
Flash Exposure Compensation
Flash exposure compensation lets you manually adjust the amount of flash illuminating the subject without changing the camera's aperture or shutter speed. This is an ideal way to balance flash and natural light when using fill flash and to correctly expose scenes or subjects that are darker or lighter than normal (middle-gray).
You can also use flash exposure compensation in conjunction with regular exposure compensation. Doing so lets you use regular exposure compensation to lighten or darken the background that's illuminated by natural light, and use flash exposure compensation to lighten or darken the subject illuminated by the flash. This is a powerful combination of exposure controls that let's you capture images just the way you want them.
Here five photos have been taken with flash. In each, the flash exposure has been changed one stop from the next image.
Flash Exposure Bracketing (FEB)
Flash exposure bracketing (FEB) is a form of automated flash exposure compensation. This mode takes a series of flash pictures exposed at slightly different settings above and below the exposure recommended by the autoexposure system. The flash output changes with each image while the background exposure level remains the same.
Flash Exposure Lock (FEL)
Flash exposure lock (FE Lock) acts much like the more familiar AE Lock. When you use this feature, a preflash is fired and the exposure system calculates the flash exposure and stores the settings. When you then recompose the scene and take the picture, it's the stored settings that are used. FE lock is extremely useful when you wish to place the main subject in a part of the picture area that is not covered by one of the camera's focusing points. It can also eliminate potential exposure errors caused by unwanted reflections from highly reflective surfaces such as windows or mirrors.