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Distance and Aperture when Using the Built-in 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 Guide Number

Sensitivity

Built-in flash guide number

ISO 100

Approx. 13

ISO 3200

Approx. 73.5

ISO 200

Approx. 18.4

ISO 6400

Approx. 104

ISO 400

Approx. 26

ISO 12800

Approx. 147

ISO 800

Approx. 36.8

ISO 25600 *1

Approx. 208

ISO 1600

Approx. 52

ISO 51200 *1

Approx. 294

*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 effective distance of the flash.

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 100 and the aperture value is F2.8 L1 = 13 ÷ 2.8 = approx. 4.6 (m)

L2 = 4.6 ÷ 5 = approx. 0.9 (m)

Therefore, the flash can be used in a range of about 0.9 m to 4.6 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 100 and shooting distance is 4 m, the aperture value is:

F = 13 ÷ 4 = 3.25

If the resulting number (3.25, 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.

5

the Using Flash