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Concepts in Photography
Flash guide number
The model number of a ash refers to the ash’s power, and the maximum
amount of light created is represented by a value known as a "guide
number". The bigger the guide number, the more light is emitted from the
ash. The guide number is achieved by multiplying the distance from the
ash to the subject and the aperture value when the ISO sensitivity is set
to 100.
Guide number = Flash to Subject Distance X Aperture value
Aperture value = Guide number/Flash to Subject Distance
Flash to Subject Distance = Guide number/Aperture value
Therefore, if you know the guide number of a ash, you can estimate an
optimum ash to subject distance when setting the ash manually. For
example, if a ash has a guide number of GN 20 and is 4 meters away from
the subject, the optimal aperture value is F5.0.
Bounce Photography
Bounce photography refers to the method of bouncing light o of the
ceiling or walls so that the light spreads evenly over the subject. Normally,
photos captured with ash may appear unnatural and cast shadows.
Subjects in photos captured with bounce photography cast no shadows
and look smooth due to evenly spread light.