Effective use of Flash

As with any other technology knowing how it works behind the scenes and what your options are can help in better utilizing it for your advantage. Flash photography has been around for more than a hundred years. It started with a dangerous and manually controlled technology that used a powder that was lit by either fire or electrical current. These flash solutions were both dangerous and hard to use since the flash was not automatically synchronized to the camera’s shutter. Modern flash units use an electronic flash tube that is synchronized with the camera’s shutter. When turning the flash on the photographer does not need to worry about flash timing – the camera takes care of it automatically.

There are two types of flash units: Internal and External. The internal flash unit is built-in to your camera. It can be controlled through the camera’s menus. Some low end cameras only allow the use of their built-in units. Some low end cameras and all high end cameras also allow the attachment of an external flash unit. External flash units are either attached to the camera’s body through a dedicated slide-in slot or are connected to the camera using a cable. They vary in strength – how much light can they generate for how long – and in mechanical characteristics – can they be tilted or skewed or are they fixed in relation to the camera’s body. Regardless of the connection type external flash units are electronically connected to the camera and are synchronized with the shutter.

When setting your flash unit to automatic mode the camera fires the flash in scenarios where not enough light is available. Many times the camera will make a wrong judgment and will either fire or not fire the flash when the opposite was needed. Also in some scenarios the camera will not be able to tell that firing the flash will actually result in a better photo. One problem when using a flash is washed out photos. When the flash is too strong or the object is too close to the camera the result is a washed out photo there are not enough details and the object appears to be too white or too bright. Another problem is a photo with too many details: in some scenarios the flash can create artificial shadows and lights which result in a photo that includes details that are exaggerated relative to their appearance in real life. For example when taking a photo of an older person skin wrinkles and imperfections can look much worse than they really are in real life.

It is important to know the limitations of the flash unit. Any flash unit has a certain amount of light that it can generate. Usually this amount can be translated to an effective range for using the flash. When trying to take a photo with the object too far – more than the flash unit range – the object will appear dark. When trying to take a photo with the object too close to the camera the object will be washed out or too white. It is important to know your flash range and make sure that your object is within that range.

If you need to take a photo with your objects not within your flash unit range it is better to turn off the flash completely and use a tripod with long exposure. Using the flash in such scenarios can fool the camera into setting a high shutter speed which results in a photo darker than a photo taken without using the flash at all.

In some scenarios the camera will not automatically fire the flash although using the flash would have resulted in a much better photo. One such scenario is taking a photo during day time when the object is shadowed. For example if the object is wearing a hat the hat can block the light from the object’s face or when the object is lit from the side the object’s nose can block the light creating a shadow. In such scenarios the flash unit can be set to “fill in” mode. The flash will be fired to fill-in those shadowed areas but it will not be fired strong enough to wash out the photo.

Another scenario is when the sun is behind the object. One example is taking a photo on the beach against a sunset. If taken without a fill-in flash the result will most likely be a silhouette of the object. If taken with a fill-in flash and the object in range the result will be a clear photo of the object against a sunset.

Comparing Built-In Flash to External Flash

Flash Heads

When it comes to physically setting up an external flash, most come with swivel and bounce heads, to allow more realistic and softer lighting effects by bouncing light from a white card or reflector above or to the side of the subject. These are things that a pop-up flash cannot do.

Zoom heads on external flashes allow for coverage adjustment when the flash is used in conjunction with a wide-angle or telephoto lens. The path of light covered by the flash will be modified to suit the angle of coverage by the lens. Ring flashes are a particular type of external flash that forms a ring around the barrel of the lens – they are best suited to macro or portrait photography where large lenses can get in the way of pop-up flashes and cause a shadow.

Bulb Power

External flashes have much more power than built-in flashes. Think of how many times it took you to learn that your built-in flash’s light fell short of the intended subject and lit only the near objects in your scene.

Metering with Flash

Modern external flashes allow exposure to be metered with TTL (through-the-lens) flash metering, which allows the unit to regulate the amount of light output in auto-exposure modes. The flash acutally cuts off light when enough has been dispensed on the subject. Flash exposure compensation allows further fine-tuning whereby adjustments can be made to allow more or less light than the TTL metering suggests. Thus, today’s external flashes only have a guide number for flash power comparisons. The guide number on a typical pop-up flash is fairly low – perhaps 40 – whereas the guide number on an external flash easily has a guide number upwards of 100 or 200. For comparison purposes, you need to understand that a guide number of 80 is four times (two stops) more powerful than 40.

Flash Proximity to Subject

External flash also allows you to distance the flash light source from the lens. This becomes very important for macro photography where pop-up flashes can actually cause shadows of the lens, based on its proximity to the large barrel. It is also more likely to cause red-eye in portrait shots, and means you cannot conveniently counteract another light source since the built-in flash is not moveable. With infrared or radio slaves, motion detectors or photo cell sensors, multiple flashes can be triggered remotely in sync, no matter how far away from the camera they are.

Fill Flash

Most accessory flashes have the ability to shoot at less than 100% power, so as to enable fill-flash in appropriate situations. Built-in flashes must be manually covered with a diffuse fabric in order to be successful at providing fill-light (e.g. brightening a flower, or combining fill-flash with slow shutter speed for fast-moving wildlife). Variable power in external flashes makes fine-tuning aperture or flash proximity to subject very easily. Some external flashes have infrared sensors that sense the distance to the subject automatically, thus synchronizing the camera to suggest a correct aperture and shutter speed.