In this article, I’ll show you how to control your background by manipulating light fall-off.
When using studio lighting, one of the most frustrating things to deal with can be backgrounds. Sure, if you have space, time and the money, you can just stock up on seamless backgrounds covering white, black and everything in between. But if you are on a budget, or are already taxing the limits of your storage space, that’s often not a viable option.
The good news is that it’s entirely possible to take a white or grey background, whether it’s a wall or a seamless backdrop, and manipulate your light so that the background appears black or any shade of grey you can imagine.
The method discussed in this article is quite easy.
Understanding how the rate of fall-off effects your lighting will grant you great control over how your background appears in your photos.
Move the light
To control your background, all that you have to do is move your light. It’s counterintuitive though. To get a darker background, you will move the light closer to your subject. For a lighter background, you would move the light further away.
This approach has the effect of changing the background; however, it also completely alters the quality of light falling on your subject.
For this demonstration, I used a small softbox (around 3×4′) placed directly in front of and above the subject. In the sequence of images below, you can clearly see that the light source is simply moved backward in increments of two feet. Also, you’ll see that the softbox was angled upwards slightly as it moves back so that it points toward the subject and not the floor.
The light source is two feet away from the subject and angled down at forty-five degrees.
At four feet, the light had to be angled upwards slightly so that it remained pointed at the subject.
At six feet, the light on the subject gets noticeably harder, but the background appears as it is in life (its actual shade).
The light source as seen 10 feet from the subject.
In terms of the background, the way this works is through light fall-off. As the light source gets closer to your subject, the rate of light fall-off increases.
In the simplest terms possible, this means that as you move your light closer to your correctly exposed subject (remember to recalculate your exposure everytime you move your light), the light reaching your background loses intensity at a higher rate, making the background appear darker.
In this progression (starting left to right) the light begins two feet away from the subject and is moved back in two-foot increments until it is 10 feet away in the right-hand frame.
For these examples, I used a middle grey background to better illustrate the dramatic changes in tonality as the light is moved.
In the first image on the left, the light is two feet away from the subject, rendering the grey backdrop nearly black. At four feet away, in the second image, the background gets noticeably lighter. By the fifth image, at 10 feet away, the grey tone of the background almost matches the subject’s light grey shirt.
Because the light was moving away from the subject in each frame, the exposure had to be metered for each change. The image on the left was shot at f/11, while the one on the right was shot at f/2.8, which is a total of four stops of difference in exposure.
Left: soft light with the light source two feet away. Right: hard light then it’s 10 feet away. Here you can clearly see the difference in the quality of light. Pay close attention to the tonal transition between the shadow and highlight areas of both images.
It’s important to note that moving the light closer, or further away, will also have a dramatic effect on how the light appears on your subject. As the quality of light is altered on the background, it also changes on your subject. Bringing it in close will change both the softness and intensity of the light on your subject, making it both brighter in terms of exposure and softer (quality of light is directly related to the size of the light source and distance from the subject).
Moving the light away from your subject will result in a lighter backdrop. Aside from that, this will also result in harder light on your subject. Just be aware that a lot of subjects won’t suit being lit with hard light and be careful with how far you go, and you should be fine.
Move the light too far back, however, and you may as well be using a small flash from a closer distance. For example, the softbox used here from 10 feet away is only barely distinguishable from a bare speedlight at a closer distance.
The end
That’s it. This technique is easy to put into practice even if you don’t yet understand the technicalities of the Inverse Square Law that makes it work. It isn’t foolproof, however, and you may want to have other tricks up your sleeve if you’re in a position where you don’t have enough space to work with.
Background lights and flags can both go a long way to helping you solve exposing your background the way you want as well. This method is just one other option to add to your skillset, hopefully bringing you one step closer to getting things right in camera.
