The trouble with on-camera flash

Learning goal

You will be able to explain, starting from the four qualities of light, why a photo shot with the flash on top of a camera or phone most often looks harsh and flat and stands in front of a dark void. You will diagnose one by one that direct flash gives hard light because it is a small source, and flat light because it comes from right beside the lens; that when the pupil is wide, light reflects back from the retina and produces red-eye; that because of the inverse square law, flash falloff blows out the person close by and leaves the far wall in the dark; and that it leaves specular highlights on shiny surfaces and oily skin. Because the source of each of these problems is the direction, size and distance of the light, you will see why giving the flash a direction is the starting point of all the following lessons.

The question

On the evening your grandmother turns eighty, the whole family has squeezed into the small living room. The candles on the cake are burning, and the chandelier on the ceiling gives a yellow, dim light. When you raise the camera the screen looks dark; you turn on the flash and press the shutter. The frame on the screen looks nothing like the room you saw: your grandmother's face is pure white and flat, the shape of her nose and chin is lost, and there are two bright spots on her glasses. The face of your young cousin standing in front has almost blown out to white, while your uncle two steps behind is buried in a dim shadow. Behind your other cousin, leaning against the wall, there is a pitch-dark, sharp silhouette of their head; the warm light of the candles and the mood of the room are completely lost. Red dots also glow in a few people's eyes.

Why do flash photos look bad? In this new part where we step into artificial light, the first job is to separate from each other the problems the top-mounted flash brings to every frame.

Context

Throughout the module where you learned to shape natural light, you always took light from an existing source and directed it: from a window, from the sky, from a reflector. Where light runs out, the photographer has to bring their own light, and the easiest way to do this is the small flash on top of the camera. But this convenience has a price: in almost all four qualities of light, the flash comes from the least favorable place.

The aim of this lesson isn't to ban the flash, but to understand why it looks bad. When you can name the problem in terms of the size, direction and distance of the light, the solution appears under the same names. The rest of the module is built on this diagnosis.

Simple explanation

Why does direct flash look hard and flat?

Direct flash is a flash that stands on top of or in the body of the camera and sends its light to the subject without hitting any obstacle. The hardness or softness of light depends on how large the source looks relative to the subject; you know this from the lesson on hard and soft light (Lesson 5.3). The camera's flash is a window a few centimeters wide; seen from a face two meters away, it is a small point, like the noon sun in the sky. That is why the edges of the shadows are sharp and the transitions abrupt.

To the hardness a problem of direction is added. The flash comes from right above the lens, from almost the same axis. When light hits the face straight from the front, the shadows fall right behind the protrusions of the face and the lens hardly sees them at all. This is flat light: the small shadows under the nose, the cheekbones and the chin disappear, and the face loses its depth and turns into a flat surface. In natural light, what gave a face shape was light coming from the side, lighting one side while leaving shadow on the other; direct flash removes this side angle.

The shadow of flat light doesn't disappear, it only escapes behind the subject. If the person is right in front of a wall, because the flash comes from a little above, the sharp-edged shadow of their head falls on the wall, right behind the head and a little below. The dark silhouette behind the cousin beside your grandmother is this escaped shadow.

Where does red-eye come from?

Red-eye is flash light entering through the pupil, reflecting back from the retina full of blood vessels on the back wall of the eye, and returning to the lens as a red glow. A dim setting makes this easier: in the dark the pupil widens, and the light going in and coming back increases. The flash standing very close to the lens also strengthens the reflection: light returns along roughly the same axis it entered on, and if the flash is right at the lens, this reflection comes straight to the lens.

That is why red-eye is seen most in small cameras and phones, in dim rooms and in people looking straight at the camera. The red-eye reduction setting of many cameras fires a pre-light before the main flash; the pupil reacts to this light and shrinks, and the reflection decreases. But this setting only eases the problem; the pre-light also pushes people to blink, and the moment can be lost. The real solution is to move the flash away from the axis of the lens; giving the light a direction is the key here too.

Why does the background stay pitch-dark?

Flash falloff is flash light decreasing quickly with distance, and it is a direct result of the inverse square law (Lesson 18.2). Because the sun is very far away, the difference between one end of a room and the other is insignificant to it; the flash, however, is only a meter or two from the subject, and even a small change in distance changes the light greatly. When the distance doubles, the light drops to a quarter, that is, it loses two stops.

Imagine your grandmother two meters away and the wall behind her eight meters away. Because the wall is four times as far, it receives a sixteenth of the light from the flash: four stops darker. When the camera sets the exposure for your grandmother's face, the wall drops almost to black. The short shutter speed also cuts off the weak light of the chandelier and the candles in the room before it is recorded; the ambient light is erased from the photo, and what remains is an island a few meters wide lit by the flash.

The same law blows out the front row in a crowded frame. The young cousin one meter away receives four times as much light as your grandmother two meters away; if your grandmother is exposed correctly, the young cousin is overexposed by two stops. The uncle behind, on the other hand, stays two stops underexposed. Instead of showing everyone at the same brightness, the flash turns distance into a difference in brightness.

Why do specular highlights stain the face?

A specular highlight is the white spot formed when a small, hard source is mirrored off a shiny, smooth surface and returns straight to the lens. Lenses of glasses, the forehead, the tip of the nose, the top of the cheek, skin that is sweaty or has moisturizer on it easily give this reflection. Because the light comes from the axis of the lens, the reflection also returns right to the lens; because the source is small, the spot is bright and sharp-edged. The two white points on the glasses and the shiny area on the forehead come from here.

Direct flash distorts differently on different skin tones. On dark skin, specular highlights build a sharp contrast with the deep color around them and stand out on the forehead and cheek as oily, grayish white spots; if the camera sets the exposure for these spots or for a light face beside them, the skin can stay darker than it should and without detail. On light skin, on the other hand, flat light erases the natural color transitions in the cheeks, and the face turns into a chalk-white surface without life. If there are two people with light and dark skin in the same frame, the one standing closer to the flash receives too much light, and a single exposure decision sacrifices one of the two; enlarging both faces on the screen and checking them one by one is essential.

Visual evidence

Before the cake is cut, you shoot the same frame once more, and this time you read each problem separately. On your grandmother's face there is no shadow under the nose; the face is like a single plane. On the wall behind the cousin's head there is a sharp-edged, dark protrusion: the shadow hasn't disappeared, it has only escaped behind. On the forehead and the tip of the nose of your grandmother's dark-skinned neighbor, two grayish white spots shine, while the cheek of the light-skinned young cousin beside them has blown out to chalk white. There are red dots in the eyes of two children. The shelves on the wall and the orange light of the candles are lost in a pitch-black void.

Then you hold your palm in front of the flash and turn its light toward the ceiling; if the flash is a model that can tilt, you point it at the ceiling. In the new frame the light now comes from above and from a wide surface: a soft shadow appears under the nose, the silhouette on the wall disappears, the specular highlights shrink, the red in the eyes fades. How and why this solution works is the subject of the next lesson; for now, just see this: the power of the flash stayed the same, only its direction changed.

Common mistakes

Summary

Direct flash on top of the camera gives hard light because it is a small source, and flat light because it comes from the axis of the lens; the face's shadows disappear, and the shadow escapes behind the subject and sticks to the wall. The same axis produces red-eye and specular highlights, while the inverse square law, through flash falloff, blows out the person close by, buries the background in darkness, and distorts different skin tones in different ways. Because all these problems come from the size, direction and distance of the light, their solutions also go through giving the flash a direction, making it larger and managing distance.

Mini assignment

In this assignment you will find and name the problems of direct flash in your own photos.

1. In a dim room, shoot someone with direct flash while they stand right in front of a wall; then move the person three or four steps away from the wall and repeat the same frame. Note how the shadow on the wall and the background change.
2. Put a frame without flash and a frame with flash side by side; mark one by one the shadows lost on the face and the ambient light lost.
3. Shoot three people standing at different distances with direct flash; roughly calculate the difference in brightness between the closest and the farthest with the inverse square law and compare it with the photo.
4. Find red-eye and specular highlights in the frames you shot with flash; next to each one write its cause and which change of direction could reduce it.

Check yourself

• Looking at a flash photo, can you name flat light, the escaped shadow and flash falloff separately?
• Were you able to calculate how many stops of brightness difference the difference in distance turned into?
• Did you enlarge the faces of different skin tones in the same frame and check how each one was distorted?

Glossary

Mini quiz

1. Why does the flash on top of the camera give hard light?

• A) Its light is a very warm color
• B) Seen from the subject, it is a very small source
• C) It lasts a very short time
• D) It is far from the lens

2. Which two conditions make red-eye easiest?

• A) Bright daylight and a long shutter speed
• B) A wide aperture and a low ISO
• C) High resolution and RAW recording
• D) A pupil widened in a dim setting and the flash being very close to the lens

3. If the person is 2 meters from the flash and the wall behind them 8 meters away, about how many stops darker does the wall stay than the person?

• A) 4 stops
• B) 1 stop
• C) 2 stops
• D) 8 stops

4. In a group photo shot with direct flash, there are grayish white spots on a dark-skinned person's forehead, and a chalk-white area on the cheek of the light-skinned person beside them. Which is the most fitting first step?

• A) Set the exposure only for the light-skinned face
• B) Look at the small preview on the screen and carry on
• C) Change the flash's direction and check both faces separately by enlarging them on the screen
• D) Get even closer to the group

Answers

1. B — The hardness of light depends on the apparent size of the source relative to the subject; a flash a few centimeters wide is a small point from two meters.
2. D — A widened pupil takes in and gives back more light; if the flash is close to the lens, the reflection returns straight to the lens.
3. A — Four times the distance means a sixteenth of the light; that is four stops.
4. C — Specular highlights and white blowouts come from light arriving hard and from the axis; changing the direction eases both, and each face should be checked separately.

Summary card

• Direct flash is a small source: hard shadows, abrupt transitions.
• It comes from the axis of the lens: flat light, an escaped shadow, red-eye, specular highlights.
• Flash falloff is the inverse square law: the near one blows out, the far one goes dark.
• A short shutter speed cuts the ambient light; the mood of the room is lost.
• The distortion differs on every skin; enlarge faces one by one.

Bridge to the next lesson

When you turned the flash toward the ceiling in the birthday room, the only thing that changed was the direction, but the result was completely different: the shadow softened, the silhouette on the wall was erased, the red in the eyes faded. How does a small flash, when it bounces its light off a white ceiling, turn into a wide, soft source? Why does pointing the flash at the ceiling work? The next lesson takes up bouncing, the ceiling and walls working like a giant softbox, and how the color and height of the surface change the light.