Tools › Exposure & light

Inverse square law

Light spreads out as it travels: twice the distance gives a quarter of the light. Enter the old and new distance of your light to the subject.

How it works

Light at the subject ∝ 1 ÷ distance². In stops: 2 × log2(new distance ÷ old distance).

The same law is why a light close to the subject falls off quickly towards the background: move the light back for a more even look.

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Change one setting and see what the others must do: equivalent exposures and the EV.

Your new shutter time with 1 to 20 stops of ND, and a countdown for bulb mode.

Sunrise, sunset, golden and blue hour for any place and day, with the sun's path.

The longest exposure for pin-sharp stars, by the NPF rule and the old 500 rule.