Samsung GX-20 ユーザーズマニュアル

104

■  A set criteria is necessary between the guide number, aperture and distance 

when shooting with the fl ash. Calculate and adjust the shooting conditions if 
fl ash is not suffi cient.

● Built-in fl ash guide number

Built-in fl ash guide number

13

18.4

26

36.7

52

The following equation calculates the aperture value for shooting distances. 

Aperture Value Used F = Guide number ÷ Shooting distance

Example)
  When sensitivity is [ISO 200] and shooting distance is 6.1 m, aperture value is:

F = 18.4 ÷ 6.1 = 3

If the resulting number (3, 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.

■  The following equation calculates the distance of the fl ash for aperture 

values.

 Maximum 

fl ash distance L1  =  Guide number ÷ Selected aperture

 Minimum 

fl ash distance L2  =  Maximum fl ash distance L1 ÷ 5*

   

*  The value 5 used in the formula above is  

  

a 

fi xed value which applies only when  

 

  using the built-in fl ash alone.

Example)
  When sensitivity is [ISO 200] and aperture value is F4

L1 = 18.4 ÷ 4 = approx. 4.6 (m)
L2 = 4.6 ÷ 5 = approx. 0.9 (m)

Therefore, the fl ash can be used in a range of about 0.9 m to 4.6 m. The fl ash cannot 

be used when the distance is less than 0.8 m. When the fl ash is used at closer than 

0.8 m, it causes vignetting in the picture corners, light is distributed unevenly and the 

picture may be over-exposed.