Flash Guide Number Distance Calculator: GN 20 m, f/1.4, ISO 400
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GN 20 m, f/1.4, ISO 400 converts to
28.57 m flash distance
Use this as a quick reference for Flash Guide Number Distance Calculator.
Value Details
Input: GN 20 m, f/1.4, ISO 400
Output: 28.57 m flash distance
Browse all reference values for Flash Guide Number Distance Calculator
aperture: 1.4 | iso: 400 | distanceFt: 93.74
Flash Guide Number Distance Calculator
Estimate flash-to-subject distance for manual flash exposure using guide number, aperture, and ISO.
Estimated Flash Distance
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Nearby Reference Values
| Flash Scenario | Distance (m) | Distance (ft) |
|---|---|---|
| GN 12 m, f/16, ISO 100 | 0.75 m flash distance | 2.46 |
| GN 12 m, f/16, ISO 200 | 1.06 m flash distance | 3.48 |
| GN 12 m, f/16, ISO 400 | 1.5 m flash distance | 4.92 |
| GN 20 m, f/1.4, ISO 100 | 14.29 m flash distance | 46.87 |
| GN 20 m, f/1.4, ISO 200 | 20.2 m flash distance | 66.28 |
| GN 20 m, f/1.4, ISO 400 | 28.57 m flash distance | 93.74 |
| GN 20 m, f/2, ISO 100 | 10 m flash distance | 32.81 |
| GN 20 m, f/2, ISO 200 | 14.14 m flash distance | 46.4 |
| GN 20 m, f/2, ISO 400 | 20 m flash distance | 65.62 |
| GN 20 m, f/2.8, ISO 100 | 7.14 m flash distance | 23.43 |
| GN 20 m, f/2.8, ISO 200 | 10.1 m flash distance | 33.14 |
Frequently Asked Questions
Common questions about Flash Guide Number Distance Calculator, formulas, and expected usage.
How do you calculate flash distance from guide number?
At ISO 100, divide guide number by aperture. For other ISO settings, multiply guide number by the square root of ISO/100 before dividing by aperture.
What does a flash guide number mean?
Guide number indicates flash power for manual exposure planning. A higher guide number generally means the flash can illuminate a subject farther away at the same aperture and ISO.
Why does ISO change effective guide number?
Increasing ISO makes the sensor more sensitive, so the same flash output can expose subjects at a greater distance. The relationship scales with the square root of ISO.
Does this replace test shots and light metering?
No. It is a fast starting estimate for manual flash setup. Modifiers, bounce, zoom head settings, and real scene conditions can change the final exposure.
Methodology and Review
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Use this page as a fast lookup reference, then confirm final project values using applicable standards and manufacturer documentation.