218
Using the Flash
9
Relationships among the guide number, aperture and distance must be
considered when shooting with the flash to obtain a correct exposure.
Calculate the shooting distance or aperture value in the following way, and
adjust the shooting conditions if the flash output is not sufficient.
The following equation calculates the effective distance of the flash for
aperture values.
Maximum flash distance L1 = Guide number ÷ Aperture value
Minimum flash distance L2 = Maximum flash distance ÷ 5 *
* The value 5 used in the formula above is a fixed value
which applies only when using the built-in flash alone.
Example:
When the sensitivity is ISO 200 and the aperture value is F5.6:
L1 = 17 ÷ 5.6 = approx. 3 (m)
L2 = 3 ÷ 5 = approx. 0.6 (m)
Therefore, the flash can be used in a range of about 0.6 m to 3 m.
However, the built-in flash in this camera cannot be used when the
distance is 0.7 m or less. When the flash is used at distances closer
than 0.7 m, it causes vignetting in the picture corners, light is
distributed unevenly and the picture may be overexposed.
The following equation calculates the aperture value for shooting distances.
Aperture value F = Guide number ÷ Shooting distance
Example:
When the sensitivity is ISO 200 and the shooting distance is 4 m, the
aperture value is:
F = 17 ÷ 4 = approx. 4.2
If the resulting number (4.2, in the above example) is not available
as a lens aperture, a smaller number that is closest (4.0, in the
above example) is generally used.
Distance and Aperture when Using the Built-in Flash
Sensitivity
Built-in Flash
Guide Number
Sensitivity
Built-in Flash
Guide Number
ISO 100
Approx. 12 ISO 1600 Approx. 48
ISO 200
Approx. 17 ISO 3200 Approx. 68
ISO 400
Approx. 24 ISO 6400 Approx. 96
ISO 800
Approx. 34 ISO 12800 Approx. 136
Calculating Shooting Distance from Aperture Value
Calculating Aperture Value from Shooting Distance
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Weight and Dimensions
