Choosing and lighting a backdrop

Learning goal

By managing its light separately from the key light, you will be able to bring a single gray backdrop to different tones, from a darkness close to charcoal to almost white. You will explain that the backdrop's tone in the photo depends less on the paper's own color than on the difference between the light falling on it and the light falling on the subject; and you will adjust this difference with the subject's distance from the backdrop, by cutting the light spill from the key light onto the backdrop, and by adding a separate background light. With the background light you will build a flat, even backdrop or a background gradient that darkens slowly behind the subject, give the gray paper color with a colored gel, and choose a matte backdrop that leaves no reflections in the photo. You will check how the relationship between the backdrop's tone and the skin's tone affects the edge and the separation on different skin tones.

The question

The band's guitarist and keyboardist come to the studio on the same day for their individual portraits. In the studio there is only one roll of mid-gray paper backdrop. The guitarist wants an almost black, charcoal-colored backdrop behind them; the keyboardist, on the contrary, imagines an almost white, airy backdrop. There is no time to buy new paper.

When you seat the guitarist right in front of the backdrop and shoot, the backdrop comes out mid-gray, just like the paper's color. When you bring them a few steps forward, the backdrop darkens, but the key light still falls on one corner of the backdrop and leaves a light patch there. When you want to open the backdrop for the keyboardist, strengthening the key light only blows out their face, while the backdrop stays the same. How does the color of a backdrop change? How can the same paper look both black and white in the same light?

Context

In the one-light portrait lesson we saw that you could darken the backdrop by moving the subject away from it (Lesson 20.1); in the multi-light pattern we also noted that a fourth light can light the backdrop separately. This lesson combines these two ideas and treats the backdrop as a separate surface managed independently of the subject.

The backdrop is a quiet but powerful part of the portrait: it largely decides whether the person will stand out or blend into their surroundings, how bright or dark the photo will feel, and the atmosphere around the person. In the studio, controlling the backdrop is most often a much cheaper and more flexible way than buying a new backdrop. A roll of mid-gray paper, with the right light, can behave like a dozen different backdrops.

Simple explanation

What does the backdrop's tone depend on?

Background tone is how light or dark the backdrop looks in the photo. The paper's own color is a starting point, but the tone in the photo depends mainly on the difference between the light falling on the backdrop and the light falling on the subject the exposure is set for. When you set the exposure for the subject's face, if the backdrop receives the same amount of light as the face, it shows its own color, that is, mid-gray. If the backdrop receives less light than the face it darkens, and if it receives more it opens up.

The simplest way to change this difference is distance: when you move the subject away from the backdrop, the backdrop moves away from the key source and receives less of the light that weakens with the square of distance; the backdrop darkens. When you bring the subject closer to the backdrop, the backdrop opens up. This way needs no extra light but is limited by the size of the studio.

Cutting the key light's share falling on the backdrop also changes the tone. Light spill is the part of a light that spills outside the intended subject, here onto the backdrop. When the key light spills onto the backdrop, unwanted light patches and uneven brightness form on the backdrop; the patch in the corner of the guitarist's portrait was this. Standing a flag on the key light's edge facing the backdrop, or putting a grid on it, makes the light fall only on the subject and lets you keep the backdrop dark.

The most flexible way, on the other hand, is to light the backdrop with its own light. A background light is a separate light used only to light the backdrop, which doesn't fall on the subject. Because its power is set independently of the key light, it changes the backdrop's tone without affecting the face. While the background light is off and the key light isn't spilling, the backdrop stays dark; as the background light is turned up, the backdrop opens slowly to gray, then to light gray, then toward almost white.

How is a background light set up?

Depending on where the background light is placed, two different looks are obtained. For a flat, even backdrop, the light is placed as two sources on the two sides of the backdrop, looking at it at about a forty-five-degree angle; the whole surface of the backdrop is lit at a brightness close to each other. This pattern is used especially when you want to bring the backdrop close to white; to make gray paper look almost white, you need to put a few stops more light on the backdrop than on the subject, and the exact value is told by the test frame and the histogram.

A background gradient is a soft transition of light in which one area of the backdrop is brighter and its surroundings progressively darker. The most common way to do this is to put a small background light right behind the subject, close to the floor, hidden from the frame, and turn it toward the backdrop. The light forms a bright area in the middle of the backdrop, behind the subject's head, and darkens slowly toward the edges. This seats the subject's head in the brightest area of the backdrop and separates it from the backdrop on its own. A gridded head narrows the bright area, a bare head widens it.

To give a gray backdrop color, attaching a colored gel in front of the background light is enough (Lesson 19.9). The gray paper takes on the gel's color: with a blue gel you get a blue backdrop, with a red gel a red one. Gray shows colors more saturated than a white backdrop, because white paper tends to turn color into a light pastel. The same roll, with a few gels, becomes a backdrop in many colors.

Which backdrop, which surface?

A matte backdrop is a backdrop that scatters the light falling on it in every direction without shining. Studio paper, dyed fabric and painted canvas are usually matte and leave no reflections in the photo. A shiny surface, for example a polished panel or a glossy paint, reflects light back like a mirror and forms bright patches on the backdrop. Fabric backdrops are prone to wrinkles; light coming from the side makes these wrinkles stand out, which is why you need to keep a fabric backdrop taut or give the light from the front. When the subject stands very close to the backdrop, the backdrop's color also reflects onto the subject: green paper can leave a green tone on the neck and the edge of the hair of a person standing at its foot.

The relationship between the backdrop's tone and the skin's tone decides how much the subject will separate from the backdrop. When dark skin and black hair come side by side with paper brought down to charcoal, the edge of the face and the hair can blend into it; opening the backdrop a little or putting a background gradient behind the head brings the edges back. When a light-skinned person stands in front of an almost white backdrop, the edges of the face can melt into the backdrop; darkening the backdrop a little or cutting the key light's spill onto the backdrop increases the separation. This isn't a rule: sometimes the person merging with the backdrop can be a deliberate choice. What matters is that the separation or the merging comes about by decision, not by chance; you check this by enlarging the edge of the face and the hair in the test frame.

Visual evidence

For the guitarist you use the farthest corner of the studio: you bring the guitarist three steps forward from the backdrop and put a black flag on the edge of the key softbox facing the backdrop. The background light is off. In the test frame the gray paper has dropped to charcoal; the light patch in the corner has disappeared. Because the guitarist's dark skin and black hair come close to the dark backdrop, the edge of their head starts to merge with the backdrop. You put a small gridded background light on the floor right behind their head and turn it on at low power. A soft brightness appears behind their head, darkening toward the edges; the curls of their hair start to be made out in front of this brightness.

For the keyboardist you set up two flashes on the two sides of the backdrop, looking at it diagonally, and set their output a few stops above the light on the face. In the first frame the backdrop is light gray; when you raise the power one more stop, the backdrop is almost white. The keyboardist's light skin and light brown hair seem to melt into this white. You turn the background lights down by half a stop; the backdrop is still airy and bright, but the keyboardist's shoulder and the edge of their hair now separate from it. The same gray roll has become two separate worlds in two portraits.

Common mistakes

Summary

The backdrop's tone in the photo depends less on the paper's color than on the difference between the light falling on the backdrop and the light falling on the subject; this difference is adjusted with the subject's distance from the backdrop, by cutting the key light's spill onto the backdrop with a flag or a grid, and with a separate background light. Two lights from the two sides of the backdrop give a flat, even backdrop, a small light hidden behind the subject builds a background gradient that brightens behind the head and darkens toward the edges, and a gel attached to the background light gives gray paper color. A matte backdrop leaves no reflections; the tonal relationship between backdrop and skin decides the separation, this relationship is built as a decision, not a rule, and the edge of the face and hair is checked by enlarging on every skin.

Mini assignment

In this assignment you will bring a single gray or neutral backdrop to different tones without buying a new one.

1. Shoot a person close to the backdrop, two steps from it and four steps from it, and see how the backdrop's tone changes with distance.
2. Shoot a frame where the key light spills onto the backdrop, then put a flag or a piece of card on the light's edge facing the backdrop and compare your frames.
3. Create four tones from dark to light by shooting the backdrop with a background light off, at low, medium and high power; if possible, build one frame with a gradient behind the head and one frame with a colored gel.
4. Draw the view from above of each setup; next to each frame write how much the edge of the face and hair separates from the backdrop.

Check yourself

• Can you explain the three ways of changing the backdrop's tone and the limit of each?
• Were you able to notice the key light spilling onto the backdrop and cut it?
• When choosing the backdrop's tone, did you look at whether the edge of the person's face and hair separates from the backdrop?

Glossary

Mini quiz

1. When the exposure is set for the face, when does a mid-gray backdrop show its own color?

• A) When no light falls on the backdrop at all
• B) When the backdrop receives the same amount of light as the face
• C) When the backdrop receives more light than the face
• D) When the backdrop is a shiny surface

2. Why doesn't strengthening the key light work to open the backdrop?

• A) The face is lit in the same proportion too and blows out; the difference between backdrop and face doesn't change
• B) The key light never reaches the backdrop
• C) The backdrop's color changes
• D) The white balance breaks

3. How is a backdrop that brightens behind the subject's head and darkens toward the edges built?

• A) By putting two lights of equal power on the two sides of the backdrop
• B) By turning the key light toward the backdrop
• C) By sticking the subject to the backdrop
• D) By hiding a small background light behind the subject, close to the floor, and turning it toward the backdrop

4. A light-skinned, light-haired person merges with an almost white backdrop. Which is one of the ways of increasing the separation?

• A) Strengthening the background lights even more
• B) Bringing the subject closer to the backdrop
• C) Turning the background lights down a little or cutting the key light's spill onto the backdrop
• D) Opening the aperture

Answers

1. B — If the backdrop receives the same light as the face, it shows its own tone at an exposure set for the face.
2. A — The key light lights both the face and the backdrop together; the difference between them stays the same, while the face blows out.
3. D — The small light behind the subject forms a bright area in the middle of the backdrop, and the edges darken.
4. C — Darkening the backdrop a little separates the edge of the light-skinned face and hair from it.

Summary card

• The backdrop's tone is the difference between the light falling on the backdrop and on the subject.
• Distance, cutting the spill and a background light: three ways of changing the tone.
• An even backdrop from both sides, a gradient with a small light from behind, color with a gel.
• A matte backdrop leaves no reflections; stretch the fabric.
• Build the backdrop-skin relationship as a decision; check the edge by enlarging on every skin.

Bridge to the next lesson

While the guitarist's and the keyboardist's portraits stood side by side, something caught your attention: in both, while adjusting the backdrop's tone, you had also kept estimating by eye the difference in light between the two sides of the face. Once you opened the fill too much and flattened the face, once you left the shadow side blind. If you could build this balance between lights not by eye but with a number, you could rebuild a portrait the same way weeks later too. How do you measure the balance between lights? The next lesson tells about the ratio between the key and fill light and the light meter used to measure it.