Inverse Square Law · Flash Power Calculator

I₂ = I₁ × (d₁ / d₂)² · light · flash · distance calculator

Change the distance → all parameters are calculated automatically · ISO · aperture · flash level · guide number

Camera settings at D1

Aperture (starting value)

ISO (starting value)

Shutter speed

Mind the sync speed (usually ≤ 1/200 s)

Flash settings

Rated power

Guide number (estimated)

at full power / ISO 100

GN —

Current flash level at D1

Distance flash → subject

D1 — original 1,0 m

D2 — new 3,0 m

Scene · top view

+6 stops (bring the light closer) ±0 −6 stops (light further away)

Calculated display, not a control — follows automatically from D1/D2 above.

Light falloff · 1/r² curve

All calculations · automatic

Intensity ratio

—

I₂ / I₁

Stops difference

—

Distance factor

—

d₂ / d₁

EV correction

—

camera side

Parameter	at D1	at D2 (required)	Change
Flash power level	—	—	—
Effective Ws	—	—	—
Aperture (leave the camera open)	—	—	—
ISO (raise/lower)	—	—	—

Guide number (full power)

GN —

ISO 100 · metres

Effective GN at D1 level

GN —

—

Range at chosen aperture

— m

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