How is it possible to replace one incident measurement with two grey card readings?

When I introduced a way to do incident metering without an incident meter I received several questions with regards to how this was possible.

Let me try to explain a bit further.

An incident light meter uses a white (but translucent) dome to integrate light from several directions:

Integral measurement

By taking two measurements with a grey card, you can approximate this quite well, actually to the point where the results are really really close.

Incidentmeter 5Incidentmeter 6

The trick is in the measurements and in the math.

More? Click here:

Incidentmeter.com

Author: Chris Marquardt

Chris Marquardt is co-author of The Film Photography Handbook and Absolut analog. He’s the host of this podcast and a few others. Chris teaches photography all over the world. He is a regular on the TWiT Network.