Light Digital Production: Flash Mode

Many digital SLR cameras are equipped with a built-in pop-up flash unit. If the camera is in auto mode, the flash will fire automatically when lighting is poor or the subject is back lit. The same is true in portrait, close-up, and other scene modes. In P, S, A, and M modes, the photographer can manually turn the flash on and off.
If the light from the flash is too bright, photographs will be too bright (overexposed) ; if it is not bright enough, photographs will be too dark (underexposed).

The illustration is an artist’s conception.

Immediately before the shutter is released, the built-in flash units in Nikon digital SLR cameras emit low-intensity flashes (monitor pre-flashes) to measure the amount of light reflected from the subject. Together with the distance to the subject, these data determine the intensity of the main flash.

Using a Flash

If a flash is not used when lighting is poor, shutter speeds will slow and photographs may be blurred. If the subject is back lit, details in shadow areas may be lost. The flash can be used to prevent blur or to illuminate details in backlit subjects.

Photo taken without flash

Photo taken with flash

These photographs of a backlit subject were taken indoors. Using the flash makes the portrait subject brighter.

Different flash modes are available to control the effect produced by the flash. These flash modes include fill flash, slow sync, and rear-curtain sync.

hese flash modes include fill flash, slow sync, and rear-curtain sync.

Fill Flash

Shutter speed is automatically set to around 1/60 s and the flash fires with each shot, brightening poorly lit portrait subjects. Because the intensity of the light from the flash diminishes with distance, objects behind the main subject will appear dark.

Slow Sync

The flash is used to light the main subject, and slow shutter speeds are used to ensure that objects in the background that are not fully lit by the flash are correctly exposed. Portrait subjects will be brightly lit and the shutter will remain open after the flash has fired to ensure that night scenery or dark interiors behind the portrait subject are correctly exposed.

The illustration is an artist’s conception.

Fill flash and slow sync

Fill flash

Slow sync

These portraits were taken against a night backdrop using a flash. The portrait subject in the photograph taken using fill flash is correctly exposed, but the background is dark. This is due to the fact that fill flash is intended only to light the main subject. In contrast, both the portrait subject and the background are correctly exposed in the photograph taken using slow sync. The shutter speed required is however extremely slow, meaning that the photographer must use a tripod and exercise caution to prevent blur.

Rear-Curtain Sync

In this mode, the timing of the flash differs from that in other modes. In other flash modes, the flash fires as the shutter opens, but in rear-curtain sync the flash fires just before the shutter closes. This ensures that light trails created by moving light sources appear to follow the moving object.

Fill flash
The light trails extend in front of the moving object.

Rear-curtain sync
The light trails follow the moving object