Nikon SB-800 instruction manual To calculate the correct aperture, To calculate the guide number

To calculate the correct aperture

Calculate the correct aperture by using this equation and the guide number table, according to the ISO sensitivity, flash output level and zoom-head position that are set:

f/stop (aperture) = Guide number (GN) x ISO sensitivity factor ÷ Shooting distance (m/ft)

•Set the same aperture on both the SB-800 and the camera or lens.

To calculate the guide number

Calculate the guide number by using this equation, according to the shooting distance and aperture required.

Guide number (GN) = Shooting distance (m/ft) x Aperture ÷ ISO sensitivity factor

•Referring to the guide number table, determine an appropriate flash output level corresponding to the guide number obtained above, then set the same value on the SB-800.

•In Distance-priority manual flash operation, the guide number (indicating the amount of light generated by the flash) is automatically determined by the SB-800 according to the distance value and aperture set.

ISO sensitivity factors

For sensitivities other than ISO 100, multiply the guide number by the factors shown in the table below.

ISO	25	50	100	200	400	800	1600
Factors	x0.5	x0.71	x1	x1.4	x2	x2.8	x4

Detailed operation

43