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Using the built-in flash, Calculating aperture value from shooting distance, Calculating shooting distance from aperture value – Samsung ER-GX20ZBBB-E1 User Manual

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Distance and Aperture when Using the Built-in Flash

■ A set criteria is necessary between the guide number, aperture and distance

when shooting with the fl ash. Calculate and adjust the shooting conditions if
fl ash is not suffi cient.

● Built-in fl ash guide number

Sensitivity

Built-in fl ash guide number

ISO 100

13

ISO 200

18.4

ISO 400

26

ISO 800

36.7

ISO 1600

52

Calculating Aperture Value from Shooting Distance

The following equation calculates the aperture value for shooting distances.

Aperture Value Used F = Guide number ÷ Shooting distance

Example)
When sensitivity is [ISO 200] and shooting distance is 6.1 m, aperture value is:

F = 18.4 ÷ 6.1 = 3

If the resulting number (3, in the above example) is not available as a lens aperture,

the smaller number that is closest (2.8, in the above example) is generally used.

Using the Built-in Flash

Calculating Shooting Distance from Aperture Value

■ The following equation calculates the distance of the fl ash for aperture

values.

Maximum

fl ash distance L1 = Guide number ÷ Selected aperture

Minimum

fl ash distance L2 = Maximum fl ash distance L1 ÷ 5*

* The value 5 used in the formula above is

a

fi xed value which applies only when

using the built-in fl ash alone.

Example)
When sensitivity is [ISO 200] and aperture value is F4

L1 = 18.4 ÷ 4 = approx. 4.6 (m)
L2 = 4.6 ÷ 5 = approx. 0.9 (m)

Therefore, the fl ash can be used in a range of about 0.9 m to 4.6 m. The fl ash cannot

be used when the distance is less than 0.8 m. When the fl ash is used at closer than

0.8 m, it causes vignetting in the picture corners, light is distributed unevenly and the

picture may be over-exposed.

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