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External flash benefits
Most compact cameras and digital single lens reflex cameras come with a small built-in flash controlled by the camera. They are convenient, lightweight, automatic and have red-eye reduction. However, unlike an external flash, a built-in flash lacks creative control, is not very powerful and at times light output can be harsh light. Because of their position close to the lens, built-in flashes can cause red eye.
External flashes prevent red eye
Red eye occurs because light from the flash comes from roughly the same place as the lens, hits the back of the eyes and bounces straight back. Red eye reduction tries to fix this by firing pre flashes to constrict the pupil, which makes the redness smaller, but not disappear.
External flashes generally eliminate this problem simply because of their distance from the lens. An external flash prevents red-eye by altering the angle that the light travels. It does this by bouncing the light off of a ceiling or wall.
An external flash can also be removed from the camera and fired from a different location.
Power
The most obvious advantage of an external flash is power. More power gives a greater range; it can illuminate a larger area and be useful at a greater distance.
An external flash has its own set of batteries enabling it to recycle (recharge and be ready) faster. This has two benefits over built-in flashes: you can take more shots instead of waiting for the flash to recycle and the flash won’t drain the cameras batteries.
Size
Admittedly an external flash is larger and more bulky than a built-in flash. If you attach one on a compact camera with a hot shoe, the flash can weigh more than the camera.
However, the size of an external flash is part of its advantage.
Think about a portrait studio. They use large strobes and even larger softboxes and umbrellas. The reason is that softness of light is a function of how large the light appears to the subject. So in the case of an external flash, the flash head is already four to ten times the size of the built-in which makes it softer. To go a step further, if the external flash tilts and swivels, it can bounce off a larger surface and become very soft and directional.
Directionality
Directionality is the greatest advantage of the external flash.
Think about on-camera flash as a copy machine. When light comes directly from the camera, we call the light flat. Flat light is ok; it has no shadows but can make people look flat and shiny.
If the flash is bounced up off of a low ceiling, there will be shadows, but they will be in the places we would expect. If the flash is swiveled to one side and bounced off of a neutral colored wall, then the result can be an attractive sidelight.
Dig deeper in your wallet and get an off-camera cord or an ir/radio remote and an external flash which can be placed almost anywhere. This kind of creative freedom opens up possibilities for lighting schemes that will allow you to create rather than copy.
Some older flashes (pre 90’s and especially 70’s) use a trigger voltage from 12 to 350 volts. Modern digital compacts and DSLRs can’t handle this kind of power (nothing over about six volts) and should never be used with older or aftermarket flashes.
Article contributed by professional photographer Brett Turner.