Diffuser and flag

Learning goal

You will be able to shape harsh sun, even though you can't change its position, either by spreading it or by cutting it. You will turn a small, hard source into a large, soft source by passing light through a translucent diffusion panel, see how the diffuser distance decides the softness and the difficulty of carrying the panel, measure how much light loss the light passing through the panel suffers and set the exposure for the face, keep light, or unwanted colors bouncing from the surroundings, from reaching an area with a black flag, give direction and shape to flat light coming from every direction with negative fill, and check how these tools change shadow, shine and color on different skin tones.

The question

You have to shoot a portrait of a friend in the park at noon; you have no other time. The sun is almost overhead, and there are sharp, short shadows on their face: a dark triangle under the nose, two dark hollows under the eyebrows, shiny spots on the forehead and the tip of the nose. You try to open the shadows with a reflector; but this time it is as if another hard light has been added to the hard light, and the face looks even shinier and more strained. Your friend squints.

There must be a way to soften the sun or hide a piece of it. How do you soften harsh sun? In this lesson we will talk about the diffuser that spreads light and the black flag that cuts light, that is, the two siblings of the reflector, which adds light.

Context

In Lesson 5.3 we saw that the hardness of light comes from the apparent size of the source, and that a sheer curtain drawn across a window turns the small sun into a large source. Indoors the curtain hangs on the wall; outdoors, a panel carried by hand does the same job. There are three basic things a photographer can do with natural light: send light back, spread light and cut light. The previous lesson told the first; this lesson tells the others.

When these three tools are used together, it becomes possible to build a face's light to a large extent, regardless of where the sun is: the diffuser softens the sun, the reflector opens the shadow, the flag cuts unwanted light. None of them needs to be expensive; a bed sheet, a white card and a black cloth most often do the job of the professional tools that fill a bag.

Simple explanation

How does a diffuser work?

A diffusion panel is a panel made of a translucent white fabric stretched over a frame, held between the sun and the subject to spread the light. When sunlight hits the fabric it scatters in every direction, and for the subject the light source is no longer the small, distant sun, but the whole surface of the fabric. Because the source grows, the edges of the shadows soften, the shiny spots on the face shrink and spread, and the sharp darkness in the eye sockets turns into a soft shadow. Direct sun, which makes the person squint, also no longer hits their eyes.

Diffuser distance is how close the panel is held to the subject, and it directly decides the softness. When the panel is close to the face, it is a large source to the subject and the light is at its softest; as the panel moves away it shrinks to the subject, the light hardens again, and beyond a point the panel only casts a shadow. That is why the panel is held far enough not to enter the frame but as close to the face as possible; usually just outside the frame, a little above the head and in the direction of the sun.

How does a diffuser change exposure?

Light loss is less light reaching the subject because part of the light passing through a diffuser is absorbed in the fabric or reflected back. This loss, which varies with the thickness of the fabric, can most often be one stop or a little more; instead of guessing, you need to meter the face while the panel is in place. The face under the panel is now darker than its surroundings: the grass, sky or buildings behind still stand in direct sun.

This difference makes the exposure decision important. If the camera meters by looking at the whole frame, it meters for the sunny background and leaves the face under the panel dark. You need to set the exposure for the face; this in turn makes the background look a little brighter, perhaps blown out. The solution to this is either choosing a darker area as the background, using a background in the panel's shadow, or accepting a bright background as a deliberate choice. On dark skin, not setting the exposure for the face leaves it without detail; on light skin, because the panel has already reduced the shiny spots, an exposure set for the face keeps the texture of the skin.

What does a flag cut?

A black flag is a panel made of black fabric or card that doesn't reflect light, and that keeps light, or light bouncing from the surroundings, from reaching a particular area. It has a few jobs. If the sun hits the lens and creates flare, a flag held just outside the frame shades the lens. If light is wanted on only part of the subject, the flag cuts the other part of the light. If colored light from the surroundings isn't wanted, the flag cuts that too: the secondary light we saw in Lesson 18.1, which grass or a red wall reflects onto a face, can largely be blocked with a black flag held on that side of the face.

Negative fill is deepening the shadow on one side of the subject by putting a black surface that absorbs light there, instead of a white surface that gathers light. In open shade or on a cloudy day, light comes from every direction and the face can look flat and shapeless. Putting a black flag on one side of the face cuts the light coming from that side and gives the face a direction, a shape. But this shadow deepens differently on every skin: a negative fill that gives a pleasing shape on light skin can quickly push the shadow side of dark skin into darkness without detail. Moving the flag a little farther away, or balancing it with a small white surface, keeps the detail while keeping the shape.

Visual evidence

The next noon you go back to the park with a helper; with you are a white fabric stretched over a frame and a black card. Your helper holds the diffuser a little above your friend's head, between them and the sun. First from two meters away: there is the panel's shadow on the face, but the light is still fairly hard. When the panel comes to half a meter from the face, the triangle under the nose turns into a soft shadow, the eye sockets into a slight darkening; the shiny spot on the forehead spreads out, and your friend no longer squints. When you meter the face you see that the panel takes about one stop of light, and you open the exposure one stop for the face; the grass behind is brighter, but the face, with the warm brown of dark skin and the eyelashes, is detailed.

Then you move to open shade, in front of the north side of a building. Light comes from every direction and the face looks flat; the reflection of the green grass has also given their cheek a slight greenness. You hold the black card on the right side of the face, one meter away: the greenness disappears, a soft shadow comes down on that side of the face and the face gains shape. When you bring the card to half a meter, the shadow side darkens too much and detail starts to disappear; you pull the card back a little and find the balance.

Common mistakes

Summary

A diffusion panel is held between the sun and the subject to spread the light and turn a small, hard source into a large, soft source; as the diffuser distance shortens the light softens, as it grows the light hardens again, and because light passing through the panel suffers a light loss of about one stop or a little more, the exposure should be set for the face. A black flag cuts sun hitting the lens, light falling on unwanted areas, and colored light bouncing from grass or a wall; negative fill, in flat light coming from every direction, gives shape and direction by darkening one side of the face. Because these tools give different results on every skin, the exposure and the flag's distance are adjusted by looking at the screen; that way both the shape and the detail of the face are kept.

Mini assignment

In this assignment you will first spread light, then cut it.

1. At a sunny noon hour, shoot someone in direct sun; then shoot again holding a white sheet or a translucent fabric between them and the sun.
2. Hold the fabric first from two meters, then from half a meter, and compare the edges of the shadows.
3. With the fabric in place, meter the face and note how many stops of light are lost; set the exposure for the face.
4. In open shade, hold a black card on one side of the face; first from far, then up close; look at how the shadow deepens and how the color from the surroundings disappears.

Check yourself

• As the fabric came closer, how much did the shadows soften?
• When you set the exposure for the face, what happened to the background and how did you balance it?
• Did the shadow the black card created keep the detail of the skin while shaping the face?

Glossary

Mini quiz

1. Why does a diffuser soften harsh sun?

• A) Because it changes the color of the light
• B) Because it scatters the light in every direction and makes the source larger for the subject
• C) Because it moves the sun farther away
• D) Because it concentrates the light

2. What happens if the diffuser is held too far from the subject?

• A) The light gets even softer
• B) The light becomes colored
• C) Nothing changes
• D) The panel shrinks to the subject and the light hardens again

3. If the face looks flat and shapeless in open shade, what does putting a black flag on one side of the face do?

• A) It gives the face direction and shape by cutting the light coming from that side
• B) It lights the face
• C) It darkens the background
• D) It warms the color

4. Under the diffuser, a dark-skinned person's face stayed dark with an exposure metered for the sunny background. What should you do?

• A) Remove the diffuser
• B) Make the background brighter
• C) Meter the face while the panel is in place and set the exposure for the face
• D) Set the ISO to its lowest

Answers

1. B — The light scatters in the fabric; for the subject the source is now the whole surface of the fabric.
2. D — A panel moving away turns into a small source; the softness decreases.
3. A — Negative fill gives flat light shape by darkening that side.
4. C — The face under the panel is darker than its surroundings; the exposure should be set for it.

Summary card

• A diffuser spreads light: the source grows, the shadow softens, the eyes don't squint.
• Hold the panel outside the frame but as close to the face as possible.
• A diffuser takes about one stop of light or a little more; meter the face, set the exposure for the face.
• A black flag cuts: flare, unwanted light, bouncing color.
• Negative fill gives flat light shape; on dark skin adjust the distance by looking at the screen.

Bridge to the next lesson

With the diffuser, reflector and flag you were able to tame the noon sun; but this took a helper and a bag full of tools. One day, with none of them with you, you will need to shoot someone at noon in a market street or on a beach. Without tools, only by deciding where to stand and how to place the person, are there ways to escape harsh sun? What do you do in the midday sun? The next lesson talks about shooting in difficult light: moving into the shade, putting the sun behind, and using open shade.