June Korea Photography: Week 01: Inverse Square Law

The Laws of Lights and How to Break Them

Instructor: Chris Callis

Week 01: Inverse Square Law
Assignment: Inverse Square Law

[Demonstration Chart]

[1]

Single ambient light source 2ft. away from the middle grey card
1/25(approx. 32)s, f/5.6, ISO 400

[2]

Single ambient light source 4ft. away from the middle grey card
1/8s, f/5.6, ISO 400

Demonstration:

1/(4ft./2ft.)² = 1/4
(light source on the object decreases to 1/4 that of the shot number 1)

In order to get the same exposure from the shot number 1,
add 2 stops (1/4 → 1/2 → 1) from 1/25(approx. 32)s, f/5.6, ISO 400
= 1/8s, f/5.6, ISO 400

[3]

Single ambient light source 8ft. away from the middle grey card
1/2s, f/5.6, ISO 400

Demonstration:

1/(8ft./2ft.)² = 1/16
(light source on the object decreases to 1/16 that of the shot number 1)

In order to get the same exposure from the shot number 1,
add 4 stops (1/16 → 1/8 → 1/4 → 1/2 → 1)
from 1/25(approx. 32)s, f/5.6, ISO 400
= 1/2s, f/5.6, ISO 400

[4]

Single ambient light source 16ft. away from the middle grey card
1.5s, f/5.6, ISO 400

Demonstration:

1/(16ft./2ft.)² = 1/64
(light source on the object reduces to 1/64 that of the shot number 1)

In order to get the same exposure from the shot number 1,
add 6 stops (1/64 → 1/32 → 1/16 → 1/8 → 1/4 → 1/2 → 1)
from 1/25(approx. 32)s, f/5.6, ISO 400
= 1.5s, f/5.6, ISO 400

[5]

Black card at the front / Grey card at the middle / White card at the rear
Make all the three cards the same 18% value of grey
1/25s, f/7.1, ISO 400

Distance:
(please see the attached production shots below to see the actual set)

In order to make all the three cards the same 18% value of grey:

Between single ambient light source and the front black card: 1.4ft.
Between single ambient light source and the middle grey card: 3.6ft.
Between single ambient light source and the rear white card: 9ft.

Between the front black grey card and the middle grey card: 2.2ft.
Between the middle grey card and the rear white card: 5.4ft.

*Camera was located at 2.9ft. away from the front black card
*Light was located in-between the camera and the front black card
(1.5ft. away from the camera, 1.4ft. away from the front black card)