GN is an acronym for “Guide Number” and is used as a specification for flash power. The higher a GN, the more powerful the flash. A GN is usually listed in feet or meters, along with an aperture and ISO: GN of 38m (125ft) @ 35mm, ISO 100. What this means is that you can get a good exposure up to 125ft with an aperture of f/1. Since most people don’t have an f/1 lens, you can use the following equation: Aperture = GN/distance. Therefore: f4 = 125’/31′.
A GN is a useful tool for comparing flashes and can help with manual flash calculations.
Please leave a comment below:
« Back to Glossary Index