Flash photography tip: Don't worry too much about the guide number

Thursday 9 February 2023, 15:51 by Elja Trum | 3,962 views | 0 comments

This article was translated from Dutch with the help of AI. Read the original.

When you buy a flashgun, it's useful to know that its maximum power is indicated by the so-called guide number. The higher the number, the more powerful the flashgun.

Depending on how you plan to use your flashgun, that maximum power may not be relevant at all. I almost never use my flashgun at its maximum setting. I usually get far too much light.

Unfortunately, not all manufacturers measure the guide number of a flashgun in the same way. Usually, the measurement is based on 100 ISO and 105mm, but sometimes 200 ISO is used, for example, or a zoom setting of 200mm, which makes the guide number higher.

The guide number of the flashgun is often included in its name. For example, the Canon Speedlite 600 EX-RT. It has a guide number of 60, at 100 ISO and 200mm.

For a hot-shoe flash that you mainly plan to use for portrait photography, a guide number between 40 and 60 is usually more than sufficient.

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About the author

Elja Trum is the founder of Photofacts and online photography course website Photofacts Academy. He has been writing about photography since 2006. Elja is also the author of (Dutch) books on composition, black-and-white photography, flash photography and portrait photography.

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Elja Trum

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