Guide Numbers For Determining Correct Aperture In - Nikon SB-28 Instruction Manual

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) = ——————————————
To calculate the shooting distance:
Flash shooting distance (m/ft) = ——————————
Guide numbers (at ISO 100: for m/ft at 20 ｡ C/68 ｡ F) in ƒ and " modes
Flash output
level
18mm
1/1 (full) 18/59
1/2 12.7/42
1/4
9/30
1/8 6.4/21
1/16 4.5/15
1/32 3.2/10
1/64 2.3/8
• 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
Guide number (GN)
Flash shooting distance (m/ft)
Guide number (GN)
f/stop (aperture)
20mm 24mm
20/66 30/98
14/46 21/69
10/33 15/49
7/23 10.5/35 11.3/37 12.7/42 15/49
5/16 7.5/25
3.5/11 5.3/17
2.5/8 3.8/13
Zoom-head position
28mm 35mm 50mm
32/105 36/118 42/138 48/157 50/164
22.5/74 25.5/84 30/98
16/53 18/59
8/26 9/30
5.7/19 6.4/21 7.5/25
4/13 4.5/15 5.3/17
70mm 85mm
34/112 36/118
21/69 24/79 25/82
17/56 18/59
10.5/35 12/39 12.7/42
8.5/28 9/30
6.0/20 6.3/21