Using flash guns offers an effective illumination for foreground objects, but when these are correctly exposed, background areas can look dark. The trick is to learn how to balance the flash output with ambient light.
Many SLRs offer a slow-sync flash mode, which combines flash with a slow shutter speed to give a balanced exposure. With Canon cameras, you can do the same by switching to av (aperture-value) shooting mode when using flash.
To fine-tune the balance, apply exposure compensation in the camera to brighten or darken the background area, then apply flash exposure compensation to adjust the foreground brightness.
Slow-sync flash can result in slow shutter speeds, so camera shake can become a problem. Increase your ISo, typically to between ISo400 and ISo1600, to enable faster shutter speeds. For ultimate control, switch to manual, as detailed below.
How to balance flash using manual mode
Step 1: Switch to manual
Switch to manual shooting mode and dial in the correct aperture and shutter speed combination for the ambient lighting conditions, using your camera’s exposure scale as a guide.
For more on how to use your shooting modes, see Dial M for… Your exposure modes exposed.
Step 2: Increase the ISO
To avoid camera shake, increase the sensitivity setting so that you can get a sufficiently fast shutter speed. otherwise the flash-lit foreground will be sharp, but the background may be blurred.
Learn more about how to know when to increase ISO.
Step 3: Adjust the flash
Adjust the aperture or shutter speed to set the brightness of the background. To govern the brightness of the foreground, increase or decrease the manual flash power setting on the flashgun.