David Hayden Photography
Seeing the light; Part 4
Going the Distance
You will often hear photographers talk about light fall-off. But what does tha mean exactly?
Light, the very essence of photography, is not a flat, uniform entity. It dances and diminishes, painting your scene with gradients of brightness and shadow. This phenomenon, known as light fall-off, is a powerful tool for photographers to sculpt the mood and story within their frames.
However, as you move the light source towards or away from the subject, the change in the intensity of the light is NOT linear. Meaning, if you double the distance from the subject to the light source, you don’t just lose ½ the light. You actually lose ¾ of the light.
It is the change in distance, not the absolute distance that matters.
The key point to remember is that it is the change in distance that affects the fall-off. For example in the images below I show two examples.
The first example shows the light fall off from 2” to 4” to 8”.
The second image shows the light fall off from 16” to 32” to 64”. What you’ll see is that the light fall-off pattern is identical. Every doubling of distance, reduces the available light by two stops.
NOTE: It’s not the distance from the camera to the subject that matters. It’s the distance from the light source to the subject that is important.
Look at the shadows.
Look again at the pictures above. Notice how fast the shadows turn from subtle to black over the course of just 4”. When the light is very close the highlights are very bright compared to the shadows and the fall off is immediate.
In the lower image where the light source starts at 16” away, the light fall-off is much more gradual. If you had a subject on the 24” line, it would get a fair amount of light even though it’s 8” away.
A practical application of this affect is using the distance between subject and the light source in relation to the distance from the subject to the background. The closer you put your subject to the background, the more the subject will tend to blend into the background. By bringing the subject closer to the light source the brighter it becomes and the more it stands out against the background.
As you can see from the examples above if the background is twice as far from the light source as the subject it will be 2 stops darker.
Studio vs Sunlight
This is all very easy to control in a studio. Put your subject a foot from the light source and the background 8 feet from the background and it will become mostly black.
Outside in sunlight however, is a different story. The sun is 93 million miles away. It’s impossible to separate your subject from the background in any meaningful way, at least in terms of relative brightness.
So, you need to do other things like add a fill flash or place the subject where it is getting the most light and the surrounding environment is in shadow. Assuming of course you want the background significantly darker than the subject.
Based on what we just discussed, how would you set the stage for these 2 images?
Inverse Square Law
What I’ve been trying to explain without getting too technical, is that application of the inverse square law of light intensity. Some rules and guidelines can easily be broken for artistic expression. The inverse square law however, is a law of physics and immutable.
Your job as a photographer is to apply what you know about it to achieve your artistic intent.
The law states that light intensity is Inversely proportional to the square of the distance.
The actual formula for the inverse square law, as it applies to light intensity in photography, is:
Intensity ∝ 1/Distance² (∝ is the symbol for proportion)
This formula essentially states that the intensity of light is inversely proportional to the square of the distance from the source. In simpler terms, as the distance from the light source doubles, the intensity of light falls to a quarter of its original value.
Here's an example of how to use the formula:
Imagine a light source with an initial intensity of 100 units. If you stand 2 meters away from the source, the intensity you experience is 100 units). If you move 4 meters away (doubling the distance), the intensity you experience will be 25 units, calculated as:
100 units / (2x the distance) squared = 100 units / 2 squared = 100 units / 4 = 25 units.
Understanding this formula can help you predict how light intensity will change in your photographs based on the distance between your subject and the light source. It can also be helpful for understanding why using a wider aperture (lower F-stop) or longer exposure time, or higher ISO is necessary when photographing subjects at greater distances from the light source.
Learn by doing!
All this discussion and math only serves to help you intellectually understand how distance affects exposure and shadows. To really get a full intuitive understanding you have to play around and practice until you don’t even need to think about it. In educational theory this is what might be referred to as becoming unconsciously competent.
Set up an object on a table or a person near a wall and illuminate with a flashlight, studio light, strobe or whatever you have that is consistent and you can control.
First set the light very close to the subject, set exposure and photograph.
Second, double the distance between light source and the subject, photograph without changing your exposure settings.
Third, without moving the light, properly expose and take a photograph.
Fourth, compare the photos. How did the exposure change? How did the shadows change? How did the brightness of the subject in relation to the wall change.
Fifth, without moving the light, move the subject very close to the light source, set exposure and photograph. Compare this photograph with the others comparing shadows, brightness of subject vs. the background and so on.
Sixth. Move the light 4 or more times the distance away from the subject but not moving the subject. Set exposure and photograph as before and again compare with previous photos.
Spend an hour or two with this exercise and you will really develop a feel for how the distance from the light to the subject and background can really change the feel of the photograph.
The next article will discuss some of what I have learned about learning.
May the images in your mind become your inspired creations!
Links to previous articles in this series.
Photography, after all, literally means drawing with light. So, this is the first of series of articles that will discuss some basic principle of light that never change and that we can use to our advantage.
Seeing the light part 1 – What’s your angle?: https://www.davidhaydenphoto.com/post/seeing-the-light-part-1
Seeing the light part 2 – All Light has Color: https://www.davidhaydenphoto.com/post/seeing-the-light-part-2
Seeing the light part 3 – Shadows tell the Story: https://www.davidhaydenphoto.com/post/seeing-the-light-part-3