Nikon FSA02911 Instruction Manual - Page 56

Guide Numbers for determining correct aperture in Guide numbers help you determine a correct exposure or proper aperture (f/stop) when using the SB-28 in the Manual ƒ or Repeating Flash " mode. • See page 51 for % guide numbers. The guide number represents the amount of light (ISO 100: for m/ft) generated by the flash. With the SB-28, you can calculate a correct aperture by using the following equation and the guide number table. To calculate the correct aperture: f/stop (aperture) = -F-laG-shu-isdhe-on-outim-ngb-edr-is(tG-anN-c)e-(m-/f-t) To calculate the shooting distance: Flash shooting distance (m/ft) = -G-uf/i-sdteo-pn-u(am-pbe-ertru-(rGe-)N-) Guide numbers (at ISO 100: for m/ft at 20ŇC/68ŇF) in ƒ and " modes Flash output Zoom-head position level 18mm 20mm 24mm 28mm 35mm 50mm 70mm 85mm 1/1 (full) 18/59 20/66 30/98 32/105 36/118 42/138 48/157 50/164 1/2 12.7/42 14/46 21/69 22.5/74 25.5/84 30/98 34/112 36/118 1/4 9/30 10/33 15/49 16/53 18/59 21/69 24/79 25/82 1/8 6.4/21 7/23 10.5/35 11.3/37 12.7/42 15/49 17/56 18/59 1/16 4.5/15 5/16 7.5/25 8/26 9/30 10.5/35 12/39 12.7/42 1/32 3.2/10 3.5/11 5.3/17 5.7/19 6.4/21 7.5/25 8.5/28 9/30 1/64 2.3/8 2.5/8 3.8/13 4/13 4.5/15 5.3/17 6.0/20 6.3/21 • Guide number varies with film speed. For example, when shooting a subject located 9m (approx. 30 ft) away at 1/1 (full) flash output, with the zoom-head position at 35mm and a film speed of ISO 100, first read the guide number from the table above. In this case, it is 36 (or 118). Then divide the guide number by the shooting distance: f/stop = 36/9 (in meters) = 4 f/stop = 118/30 (in feet) = 3.93 = approx. 4 Therefore f/4 is the correct aperture. 56