Flash Guide Number (at ISO 100)
Settings
Aperture
Results
Effective GN
58
at ISO 100, 1/1 (Full)Max Distance
10.4 m
at f/5.6Quick Reference at GN 58
| Aperture | Max Distance |
|---|---|
| f/1.4 | 41.4 m |
| f/2 | 29 m |
| f/2.8 | 20.7 m |
| f/4 | 14.5 m |
| f/5.6 | 10.4 m |
| f/8 | 7.3 m |
| f/11 | 5.3 m |
| f/16 | 3.6 m |
| f/22 | 2.6 m |
Guide Number Formula
- GN = Distance × Aperture
- Distance = GN ÷ Aperture
- Aperture = GN ÷ Distance
- ISO adjustment: GN doubles when ISO quadruples (×2 per 2 stops)
- Power adjustment: Halving power reduces GN by √2 (≈0.7×)