178Distance 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 a correct exposure. Calculate and adjust the shooting conditions if the flash output is not sufficient.

Sensitivity

Built-in Flash

Sensitivity

Built-in Flash

Guide Number

Guide Number

 

 

ISO 100 *1

Approx. 12

ISO 3200

Approx. 64

ISO 200

Approx. 16

ISO 6400

Approx. 96

ISO 400

Approx. 24

ISO 12800 *1

Approx. 128

ISO 800

Approx. 32

ISO 25600 *1

Approx. 192

ISO 1600

Approx. 48

 

 

*1 This can be used when [3. Expanded Sensitivity] in the [ACustom Setting 1] menu is set to [On].

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, light is distributed unevenly and a 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.