Page 136 - (DK) Advanced Photography Guide

134 INTRODUCING |

FLASH

Flash is an effective way to add light to a scene, either as the single source of

illumination or as a fill light to control the level of contrast. All flashes work in the

same way. The flash head is a chamber filled with xenon gas. When the flash is
triggered, an electrical pulse excites the gas so that it releases energy in the form

of light. The power of a flash is described by its Guide Number (GN): the higher

the Guide Number, the greater the distance lit by the flash.

Flash exposure
There are three variables that control the effective the shorter the effective range. The range can be
range of a flash: its GN, the aperture setting, and the increased by using a large aperture or raising the ISO.
ISO. (Shutter speed only controls the exposure of The amount of light that the flash emits is controlled
those areas of a scene that are not lit by flash.) The either by using the Manual flash exposure mode or
smaller the aperture setting and the lower the ISO, the camera’s Through The Lens (TTL) metering.

MANUAL EXPOSURE MODE TTL MODE

In Manual exposure mode, you set the flash exposure by In TTL mode, the camera calculates the flash exposure by
varying the power setting. At 1/1 the flash fires at full power. firing a preflash. The camera sets the power of the flash, then
At 1/2 the power output is halved, reducing exposure by the flash fires again to make the exposure.
1-stop. Power can usually be reduced to 1/128.
◾ ◾ Exposure is calculated by a handheld meter and can also ◾ ◾ Use when there is no time to set flash exposure manually
be determined by shooting test shots ◾ ◾ Adjust flash power using Flash exposure compensation
◾ ◾ Lower power settings reduce the recycling time ◾ ◾ The exposure is not as consistent as Manual exposure flash

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