Flash Guide Number Aperture
A guide number relates direct flash distance to aperture at specified flash and ISO settings.
Flash Guide Number Aperture
Lighting · 2 inputs
How to use this calculator
- Enter guide number in m at selected ISO.
- Enter subject distance in m.
- Select Calculate and keep the output unit with the answer.
Before you use the answer
Keep capture settings, physical dimensions and delivery requirements in separate columns of the job notes. A mathematically equivalent setting may change motion blur, depth of field or noise. Check an actual frame before committing an entire session to a numerical estimate.
Bounce, diffusion, zoom setting and manufacturer test conditions affect the usable guide number.
Does it save my inputs?
No calculation history is stored by this website. The calculator works locally in your browser. See the privacy policy for hosting and contact details.
Why might a result be approximate?
Measurement uncertainty, ideal-model assumptions and floating-point rounding can all matter. Displaying more digits does not improve the original measurement.
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