Yashica CONTAX RTS Gebrauchsanweisung Seite 70

FLASH EXPOSURE (II)
Correct Exposure Setting in Flash Exposure
Correct exposure in flash photography is determined on the basis of
the guide number of the electronic flash unit or flashbulb in use. To
obtain the aperture setting ensuring correct exposure , divide the
guide number of the electronic flash unit or flashbulb in use by the
flash-to-subject distance (in feet or meters) .
(Guide Number -'- Flash -to-Subject Distance
=
Correct Aperture)
When the guide number is given in meters , convert the flash -to-
subject distance into meters and then divide.
Example with GN 20 electronic flash unit
When shooting a subjectat adistanceof 5meters by using an ASA 100
film and an electronic flash unit with a guide numberof 20 (ASA 100 in
me ters) , the correct aperture will be:
20 (GN) -'- 5 (Distance in meters)
=
4 (F4)
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