External flash units
External flash units, also known as accessory flashes, offer much more versatility and power than a built-in camera flash. The benefits are many: increased flash range, more control of light direction, faster recycle times and they virtually eliminate red eye.
External flashes are typically mounted on a camera with a hot shoe, though they can also be used with a flash bracket attached to the tripod mount on the bottom of most cameras. Some units can be used as a wired or wireless slave flash, which fires when the built-in flash goes off. A slave flash, which requires no hot shoe, is placed away from the camera.
“Dedicated” external flashes are made to work with a specific digital camera.
External flash features
Basic external flash units offer automatic and manual flash settings. More advanced units have heads that can be swiveled and/or tilted up or down to bounce the flash and diffuse the light, or change its direction. Some external flashes have zoom heads that can be changed to match the focal length of a camera lens.
Most external flashes come with a built-in or attachable diffuser to tone down harsh lighting and expand the flash coverage when taking wide-angle shots.
One of the main reasons people buy an external flash with a bounce head is to eliminate strong light and harsh shadows that appear in photos taken with a built-in flash. The angle of the head is positioned upward so the flash can be bounced off a white ceiling or reflector, diffusing the light to produce a photo with a natural, softer look. This less harsh lighting is perfect for photographing people, or subjects such as insects for Extreme Macro photography.
A word of caution about older external flash units
Due to differences in voltage, using an older flash can damage a newer camera beyond repair. Adapters may be available so an older flash can be safely used.