Lighting 102: Understanding Soft Light
So what is it that actually makes a light soft? And why is it a function of both size and distance?
In the portrait above, Dean is being bathed in soft umbrella light from camera right. But let's zoom in a little closer and place some waypoints on his forehead...
To understand soft light, pretend for a moment that you are an ant. Specifically, pretend you are an ant on Dean's forehead. And you are standing at the rightmost of the three red dots.
His face is being lit by a flash in an umbrella, in very close. If you are at the right red dot, at this moment, you are in the full light of the umbrella. And that's simply because you can see the whole umbrella from that dot.
But what if you started to walk towards camera left, over to the shadow side of his face? What then?
As you get to the middle dot, you lose sight of trailing edge of the umbrella. That's because the umbrella is acting like the sun (albeit a very large, close sun) in a sunset. And for you at this location, the sunset is beginning.
As you continue to walk towards his shadow side, you see less and less of the umbrella/sun. You are now walking through the transition from light to shadow. And since the close-in umbrella looks very big to you, this transition will take a little time and distance. This is a signature of a soft light source.
As you keep walking away from the umbrella, you get to the leftmost red dot. At that point, the leading edge of the umbrella also disappears from your view. And you pass into the Shadow Lands.
Predicting Your Soft Light Transition
The location and softness of the transition from light to dark on your subject's face is the biggest variable in the quality of your lighting. How can you tell, without a modeling light, exactly where this transition is going to happen? And how can you tell how soft it will be?
As it happens, that's really easy. Just have your subject face the camera (or wherever they are going to face in your photo) and step over to your key light. Let's say, for example, that you are using an umbrella. Now, view them from each side of the umbrella.
The difference between what you can see of your subject from each different side of your umbrella is going to show you, exactly, the zone of transition from light to dark.
A Function of Size and Distance
As as ant walking across the subject's face, it is now easy to understand why both absolute light size and light distance both affect softness. Because they both affect how the light looks to you, the ant, as you walk from fully lit areas into areas of darkness.
Softness is not just about how big your light actually is. It's how big your light appears from the perspective of subject.
Next: Understanding the Four Zones of Light
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