Pentax AF540FGZ - Manual (Page 82)

80
Flash Effective Range
■ Calculating the Flash Effective
Range
When setting the lens to manual f/stop, calculate the
guide number at full flash with the use of flash's zoom
position and ISO. Divide the resulting guide number by
the aperture in use. Thus, the maximum distance is
obtained. The minimum distance is obtained in dividing
this max. distance by approx. 10.
However, if the minimum distance obtained is 0.7m or
less, the minimum distance will be 0.7m. Refer to page
82 for the guide number table.
Example:
With a 85 mm lens at f/4 and sensitivity at ISO100
 For the zoom position 85mm and sensitivity at ISO100, the guide number is 54.
 54 (guide number) /4 (aperture) = 13.5m (max. distance)
 13.5m (max. distance) /10 = 1.35m (min. distance) Thus, flash effective range is approx. 1.35m - 13.5m.
00_AF540FGZ.book Page 80 Monday, April 10, 2006 11:42 AM