Pentax q Operating Guide

214

Usi
ng

 th

e F
lash

10

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

PENTAX Q_ENG.book  Page 214  Monday, August 29, 2011  8:43 AM