
11-17
11
Flash
Guide Numbers for Determining the Correct Aperture
Guide numbers help you determine a correct exposure or proper aperture (f/stop) when
using the SB-28D in the Manual or Repeating Flash mode.
The guide number represents the amount of light at ISO 200 for meters/feet (m/ft)
generated by the flash. With the SB-28D, you can calculate a correct aperture or desired
flash shooting distance by using the following equations and the guide number table.
Calculating the Correct Aperture
Calculating the Shooting Distance
Guide Number Table
Guide Numbers in meters/feet at ISO 200 in Manual and Repeating Flash modes.
Flash
Output
Level
Zoom-head position
18mm 20mm 24mm 28mm 35mm 50mm 70mm 85mm
1/1 (full) 25/84 28/93 42/139 45/148 51/167 59/195 68/223 71/232
1/2 18/59 20/66 30/98 32/105 36/118 42/138 48/157 50/164
1/4 12.7/42 14/46 21/69 22.5/74 25.5/84 30/98 34/112 36/118
1/8 9/30 10/33 15/49 16/53 18/59 21/69 24/79 25/82
1/16 6.4/21 7/23 10.5/35 11.3/37 12.7/42 15/49 17/56 18/59
1/32 4.5/15 5/16 7.5/25 8/26 9/30 10.5/35 12/39 12.7/42
1/64 3.2/10 3.5/11 5.3/17 5.7/19 6.4/21 7.5/25 8.5/28 9/30
M
f/stop (aperture) =
Guide number
Flash shooting distance (m/ft)
flash shooting distance (m/ft) =
Guide number
f/stop (aperture)