Use the Book Light Technique to Achieve a Wonderfully Soft Key Light
Sometimes you need to create a nice, soft key light for your subject, whether it be for a sit-down interview or b-roll. There are a number of ways to do this, but one of the best is the Book Light technique.
First, it's important to understand that creating a soft light source is a bit counter-intuitive. One might think that you need to use a smaller light source and then move it AWAY from the subject and then dim it in order to create softness. However, the opposite is true. You actually want to use a large light source and then move it CLOSER to the subject as a starting point for creating a soft key light.
From there, you want to diffuse the light as much as possible to soften it up. The Book Light technique is an excellent method for diffusing the light. Here's what you need to do:
As stated above, use a large light source and move it close to your subject. In the picture, I'm using a 1x1 Bi-Color Astra LED panel at 100% undiffused, which is the equivalent of a 750W fresnel.
Turn the light source AWAY from your subject and aim it into a bounce card or large flex fill.
Diffuse the reflected light with opal or a silk (or both, if necessary).
Here's a diagram to show the set up in more detail.
The result is an incredibly soft light source that wraps around your subject nicely.