Flash guide numbers (don't count on it)

Started May 18, 2004 | Discussions thread
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Shay Stephens Forum Pro • Posts: 12,091
Flash guide numbers (don't count on it)

Out of curiosity and need (planning a shoot) I decided to verify the guide number (GN) of the Sunpak 383 flash. Sunpak reports the GN at 120 (feet) when using ISO 100. I measured it at 80, over a 1 stop difference in brightness at 10 feet.

If you have a flash meter and want to test your own flash, set the meter 10 feet away from the flash unit. Set the flash to manual and fire it at full power directly at the meter. Now multiply the aperture displayed by the meter by 10 (aperture X distance = GN). It may be interesting to post your results in this thread. Just note the flash and the measured GN.

My results:
Sunpak 383 advertised GN = 120, measured GN = 80

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