Page 137 - (DK) Advanced Photography Guide

FL A SH 135

Flash power
SYNC SPEED
The electrical energy to fire the flash is stored in a
capacitor, which is recharged by the batteries of Flash can be used with any shutter speed up to the sync
speed—usually between 1/150 and 1/250. If the sync speed
the flash or camera after use. The time it takes to is exceeded, the flash cannot illuminate the scene evenly,
recharge is known as the flash recycling time; this is resulting in a dark band across the image. External flash
affected by the flash power setting. The flash cannot often has a High Speed Sync (HSS) mode that makes it
be fired again until the capacitor is fully recharged. possible to use shutter speeds higher than the sync speed.

THE INVERSE SQUARE LAW

When a flash fires, the light spreads out in a cone shape,
reducing in intensity as it travels. The amount that the light
diminishes is described by the inverse square law. This means
that an object that is 3ft (1m) away from the flash, for
example, will receive four times more light than one
that is 6ft (2m) away.

FLASH

Every time the distance doubles, the
flash exposure has to be quadrupled.
To do this, you increase it by 2-stops.

DISTANCE 3 feet 6 feet 9 feet

FLASH 1/1 1/4 1/9
BRIGHTNESS 100% 25% 11%
◾ ◾ The inverse square law applies for
any flash exposure setting
◾ ◾ The flash-to-subject distance
determines the flash exposure
◾ ◾ Alter the illumination by changing
the flash-to-subject distance
◾ ◾ The background receives less light
from the flash than the subject
◾ ◾ Light-diffusing accessories reduce
the effective distance of the flash LIGHT DIMINISHES

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