Using an External Flash
A handle mounted flash with remote control. Metz flash courtesy of Bogen.
Ring flash used in closeup photography. Courtesy of Nikon.
One new variant of the ring flash is Canon's Twin Lite that has two adjustable flash heads. It's almost like a camera mounted studio.
To increase the range of your flash, or to overcome the limitations of a built-in flash, you can add an external flash unit. When one of these flash units is designed to work with the camera model you are using, it's call a dedicated flash. The camera's exposure system controls both the internal and dedicated external flash by immediately cutting off the flash when the right exposure has been reached. Flash units not specifically designed to work with your camera usually fire at full-strength so you have to control the exposure using the camera's aperture setting. Dedicated flash units also zoom the beam of light they emit along with the lens. As you widen the angle of view, the flash beam expands to cover the increased area. As you zoom in, the flash beam narrows to retain coverage but increasing the useful range.
A dedicated shoemounted flash. Courtesy
One of the biggest advantages of an external flash is that you can swivel and rotate the flash head to bounce light off walls, ceilings, or reflectors. This softens the light, fills shadows, and spreads the light over a much larger area. Subjects in the background are much lighter than they would be with direct flash. Bounce flash travels a much longer path to the subject so it's range isn't as great as direct flash. You may find many rooms too large, or ceilings too high for bounce flash to work effectively unless there is something else large and bright to bounce the light off of. Bounce flash also consumes more of the flashes's charge, so recycle times get longer.
The two most common kinds of external flash units are the hot shoe mounted and handle mounted varieties. The handle-mounted flash units are usually more powerful.
A special kind of flash is the ring flash. These units fit around the lens and fire
a circle of light on the subject. They are ideal for shadowless close-up photography
common in medical, dental, and nature photography. Because ring flash is so flat (shadowless), most units allow you to fire just one side or the other so the flash casts shadows that show surface modeling on the subject. If you happen to be selling or collecting scorpions or fireflies, one side benefit of ring flash is that it freezes action. That frisky beetle or windblown blossom can be photographed as if it were frozen in time.