Manual Flash Planner

Flash
Guide Number Calculator

Master manual flash exposure in any situation.

Flash & Camera Settings

Guide Number (at ISO 100, full power)

GN 40

Flash Power

ISO

Subject Distance

3.0 m

Your Aperture

Flash Reach — Optimal distance zone for your settings

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Effective GN

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Aperture Needed

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Max Distance

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Exposure Delta

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Calculations use GN = Distance × Aperture (ISO 100 baseline). Power fractions reduce GN by √(fraction).