Page 146 - (DK) Advanced Photography Guide

144 EXPLAINING | MANUAL FLASH

USING MANUAL EXPOSURE

EXPOSURE FLASH APERTURE f/2.8
For every stop that you
make the aperture
Unlike with TTL settings, manual flash puts you in full smaller, the effective
range of the flash
control of flash exposure, with no automation to guide decreases by about a
you. This means that it is not ideal for situations where third. To maintain the
the flash-to-subject distance is likely to change often, same level of exposure,
you either need to raise
such as at social events. Once you understand the the ISO by one stop or
relationship between the effects of aperture, flash double the power
output of the flash.
power, and ISO, however, and have had some practice,
manual flash becomes surprisingly intuitive to use.

FLASH POWER
When to use manual exposure flash Every time you halve full
The TTL flash setting is convenient but, just like the camera the flash power, you
exposure meter, it can make mistakes with exposure when reduce the effective
the reflectivity of a scene is lower or higher than average, range of the flash by
about a third. However,
and the results can be frustratingly inconsistent. Manual flash the advantages of doing
will not vary in exposure once you have correctly set aperture, this—if you open up the
flash power, and ISO. With manual flash, you also have more aperture or increase the
control over the duration of the flash—through the amount ISO—are a shorter flash
duration, a faster flash
of light emitted by the flash—than in TTL. This is vital for recycling time, and
techniques such as freezing movement using high-speed flash. slower depletion of
the flash batteries.
FLASH DURATION
Set at full power, the burst of ISO
light emitted by a flash lasts Raising the ISO setting 100
for about 1/800 second. If you increases the effective
halve the power, this shortens range of the flash. For
to 1/1600 second. The lower every doubling of the
the power you use to achieve ISO, the effective range
a correct exposure, the more increases 1.4x; to
the flash freezes movement. The double the effective
faster that your subject moves, range, the ISO needs
the lower the power you to be quadrupled.
need to use. But as lower Increasing the ISO will
power shortens the range also affect the exposure
of the flash, you may need of areas not lit by flash,
to set a larger aperture, a making them brighter.
higher ISO, or both.

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