Hoya H01-201106 - Manual (Page 216)

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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 ÷ 6 *
* The value 6 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 F2.0
L1 = 7 ÷ 2.0 = approx. 3.5 (m)
L2 = 3.5 ÷ 6 = approx. 0.6 (m)
Therefore, the flash can be used in a range of about 0.6 m to 3.5 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.
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 3 m, the
aperture value is:
F = 7 ÷ 3 = approx. 2.3
If the resulting number (2.3, in the above example) is not available
as a lens aperture, a smaller number that is closest (2.0, in the
above example) is generally used.
Depending on the lens used with this camera, even if a lens without a hood
is attached, the use of the built-in flash may not be available or may be
limited due to vignetting.
Unavailable due to vignetting
Calculating Shooting Distance from Aperture Value
Calculating Aperture Value from Shooting Distance
Lens Compatibility with the Built-in Flash
Lens Name
03 FISH-EYE