Nikon SB-28 instruction manual TTL Auto Flash t Mode, Guide number at ISO 100 for m/ft

TTL Auto Flash t Mode

For cameras in Group I: F5 only

Flash shooting distance range in 1/300 TTL High-Speed Flash sync operation (F5 only)

In combination with the F5 camera, 1/300 High-Speed Flash Sync (with Custom Setting; 1/250 sec. at normal setting) is possible. But the farthest flash shooting distance cannot be read from the indicator bars _ on the SB-28 in TTL Auto Flash t Mode.

In this case, use the guide number table and equation for calculating this distance according to each zoom-head position.

Guide number (at ISO 100 for m/ft)

Zoom head position	18mm	20mm	24mm	28mm	35mm	50mm	70mm	85mm
Guide number	8/26	8/26	11/36	12/39	14/46	16/53	18/59	19/62

Guide number

D (farthest flash shooting distance) = ——————————

f/stop (aperture)

For example, when shooting with ISO 100 film, at a 35mm zoom-head position and an aperture of f/5.6:

D = 14/5.6 = 2.5 (measured in meters)

D = 46/5.6 = 8.2 (measured in feet)

The farthest flash shooting distance is 2.5m (8.2ft). You can read the closest shooting distance from the SB-28’s indicator bars _.

•For film speeds other than ISO 100, multiply the figures in the table above by the factors shown below.

ISO film speed	25	50	200	400	800
Factor	x 0.5	x 0.71	x 1.4	x 2	x 2.8

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