Many advanced compact digital cameras and all digital single lens reflex cameras are capable of using an external flash. An external flash can be one of the most useful accessories when taking photos in less than desireable light.
If your camera has a hot shoe, it will accept an accessory flash. Here are five top reasons to use one.
Less likely to create “red eye”
Red eye is caused by the flash reflecting off of the lining of the inside of the eye. It is more likely to happen if the flash is close to the lens of the camera. Most built-in flashes have a “redeye reduction setting. This attempts to constrict the pupil to reduce the effect of redeye but can’t over come it completely.
The external flash is usually higher up and this helps some but you can also bounce the light to eliminate redeye completely. You can also use an accessory cord to move the flash away from the lense axis.
Most external flashes have the ability to tilt and or swivel the flash head. If you have a low white ceiling the flash head can be pointed up to direct light to the ceiling then back down to the subject of the photo. This works pretty well as we expect to see light coming down from above and it eliminates red eye. You can also bounce light off of a near by white wall for a nice sidelight look.
Just remember that the further away the ceiling or wall is the more power will be needed. Remember, too, that the flash takes on the color of what ever it hits.
The built-in flash in a compact or DSLR camera is nowhere near as strong as a good external unit. This means an external flash will be effective at ranges the built-in flash couldn’t hope to match.
Flash power is usually expressed as GN (guide number) this is supposed to indicate the distance in meters at which the flash is effective. The built-in flash likely has a 10GN where as most external flashes start at least at GN42
More options, more toys
Depending on the flash and camera manufacture, you may be able to control the flash while it is off of the camera. Nikon refers to this as CLS (creative lighting system) Canon calls it wireless ETTL. This allows for using the flash from a different angle or for using multiple flashes for studio style lighting.
As with all photographic items, there are accessories for the accessories. You can get extenders to increase the range of the flash, gels to change the color, diffusers to scatter, bounce card and soft boxes/umbrellas to soften, grids and barndoors to restrict and shape the light.
Best reason to get an external flash: creativity
The more power, control and options you have the more you can experiment and learn to do something cool with your camera.