160Distance and Aperture when Using the Built-in Flash

5

the Using Flash

Relationships between the guide number, aperture and distance must be considered when shooting with the flash to obtain the correct exposure. Calculate and adjust the shooting conditions if the flash output is not sufficient.

ISO Sensitivity

Built-in Flash Guide Number

ISO 200

Approx. 16

ISO 400

Approx. 24

ISO 800

Approx. 32

ISO 1600

Approx. 48

ISO 3200

Approx. 64

ISO 6400

Approx. 96

Calculating Shooting Distance from Aperture Value

The following equation calculates the 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 F4.0

L1 = 16 ÷ 4.0 = approx. 4 (m)

L2 = 4 ÷ 5 = approx. 0.8 (m)

Therefore, the flash can be used in a range of about 0.8 m to 4 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 closer than 0.7 m, it causes vignetting in the picture corners, the light is distributed unevenly and the picture may be overexposed.

Calculating Aperture Value from Shooting Distance

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 5 m, the aperture value is:

F = 16 ÷ 5 = 3.2

If the resulting number (3.2, 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.