Frozen moment, flowing motion

Learning goal

You will be able to use shutter speed on purpose to tell of movement. You will estimate the rough times needed to freeze a moment according to the subject's speed and the direction of its movement, use long times with a steady support to turn water into silk and lights into lines, try panning, which blurs the background by following a moving subject, make the choice between freezing and letting things flow according to the feeling the photo wants to tell, and predict how people will look in long times and how faces of different skin tones will be recorded.

The question

Imagine putting two photos of a waterfall side by side. In one, the water is like thousands of glass beads hanging in the air; every drop is separate, every splash sharp. In the other, the same water is like a white veil gliding over the rocks; there are no drops, only a soft flow. The two photos were taken in the same place, on the same day, with the same camera.

Why do waterfalls look like silk in some photos? Because the difference between the two frames is how long a moment the water was recorded on the sensor: a short time freezes the water, a long time lets it flow. In this lesson we will treat this decision as a storytelling tool and talk about what freezing and letting things flow tell in which situations, and how to shoot them.

Context

In Lesson 8.4 you saw how shutter speed is read and how to avoid unwanted blur. Movement was a problem there: a shaking hand or a fast-moving subject spoiled sharpness. In this lesson we use the same movement as material. A photo is a still image; but it can carry the trace of time. A short time shows the viewer a moment too short for the eye to see, while a long time fits the flow of time into a single frame.

The photo itself tells which one is "right". Freezing the moment a child jumps into the air shows the joy of that moment, the nimble body, the hair hanging in the air. Letting the same child flow a little, on the other hand, makes you feel speed and movement. Freezing motion examines a moment; letting it flow tells of a process. Both are legitimate, two separate tools a photographer holds in two hands. In this lesson you will learn to control both.

Simple explanation

How short a time do you need to freeze a moment?

The time needed to freeze a moment depends on how fast the subject is moving and how big it looks in the frame. To give a rough idea: for a walking person, around 1/250; for a running child or a bicycle, between 1/500 and 1/1000; for splashing water drops or a bird flapping its wings, 1/1000 and shorter. These aren't exact limits but starting points; zooming in on the screen and looking is always the most reliable measure.

The direction of motion matters too. A subject crossing from one edge of the frame to the other travels a long way across the sensor and blurs quickly. A subject moving toward the camera or away from it, on the other hand, changes position very little in the frame and can stay sharp at a longer time. The bigger the subject is in the frame, that is the closer you are to it or the longer your lens, the bigger the trace the same movement leaves on the sensor. Because short times gather little light, freezing often calls for plenty of light, a wide aperture or a higher ISO.

How do you let water and light flow?

To let things flow, you lengthen the time. In a stream or a waterfall, water starts to soften at around 1/15 and takes on a silky look between half a second and a few seconds. The headlights of cars passing on a road at night turn into long, unbroken lines of light in a time of a few seconds; this is called a light trail. The spinning lights of a funfair or the foam of waves on a shore leave similar traces in long times. This motion blur is the opposite of freezing: you let movement draw on the sensor.

At times this long, the camera must be completely still; otherwise not only the water but everything blurs. A tripod, a wall, a stone or a bag keeps the camera steady. Because the camera can shake even when you press the shutter button, using a self-timer of a few seconds is a good habit. Using long times in daylight is hard, though, because too much light is gathered and the photo turns pure white. Stopping the aperture down and lowering ISO to its lowest helps to some extent; for longer times, you will see filters that cut light in a later module.

What is panning?

Letting things flow doesn't always target the subject; sometimes you keep the subject sharp and let the background flow. This is called panning. You follow a cyclist passing in front of you, a running dog or a car with your camera; as the subject moves you turn the camera at the same speed and press the shutter button in the middle of the turn. The time is around 1/30 or 1/60. Because the camera moves with the subject, the subject stays relatively sharp; the still background turns into horizontal lines.

The result is a frame that gives a sense of speed even in a still photo. Panning rarely works on the first tries; many frames come out blurred. Turning your body from the hips, starting to follow the subject early and continuing to turn after you press the shutter button raise the success rate. A colorful, detailed surface in the background, for example graffiti or a row of trees, shows the flow more clearly. In front of a plain sky, panning leaves almost no trace.

What does a long time do to people?

In long times, moving people look strange in a photo. In a shot of a few seconds, someone walking past turns into a semi-transparent ghost or disappears completely; a crowded square can look empty. If you want to photograph someone in front of a waterfall with a long time, that person needs to stay still throughout the shot. The smallest head movement softens the face; even blinking can make the eyelids look semi-transparent.

When light is scarce, you need to balance freezing a face against gathering enough light. When trying to catch the texture of a dark face in dim light, lengthening the time is the first solution that comes to mind; but the longer time blurs the face. Here, keeping the time short enough to freeze the face and taking the light from the aperture or ISO gives a better result. On light skin, on the other hand, a long time can make the bright areas overflow; while the water turns to silk, the forehead and cheeks can turn pure white. If there are people in a long time, you need to check the face separately as well as the water.

Visual evidence

Imagine photographing a girl sitting on a rock in front of a village waterfall. First you shoot handheld at 1/1000. The water is frozen in the air; every drop a separate bead, the splashes hitting the rocks hanging as sharp lines. The girl's face is sharp too; her sun-browned skin, her face laughing at the coolness of the water and her wet strands of hair can be made out.

The waterfall is in deep shade; you place the camera on a stone, set the aperture to its narrowest and ISO to its lowest, turn on the self-timer and shoot at one second. You ask the girl not to move. The water is now a white veil gliding over the rocks; no drops, only a soft flow. The girl's body and face are sharp, because she didn't move; only a few strands of hair blown by the wind have turned into a light haze. Finally you photograph a child cycling past in front of the waterfall at 1/30, turning the camera with them: the child is sharp, while the waterfall and trees behind have turned into horizontal white and green lines. The same place, three times; one examines the moment, one the flow, one the speed.

Common mistakes

Summary

Shutter speed is the tool for telling of movement: short times freeze a moment and show what the eye can't see, while long times fit the flow of time into a single frame by turning water into silk and headlights into light trails. The time needed to freeze depends on the subject's speed, direction and size in the frame; letting things flow needs the camera to stay still, and panning needs the camera to turn with the subject. In long times people stay sharp if they don't move and turn into ghosts if they do; in dim light, taking the light to freeze a face from the aperture or ISO rather than from the time keeps skin in every tone better.

Mini assignment

In this assignment you will tell the same movement in three different ways.

1. Find flowing water, which could be a tap, a fountain or a stream, and photograph it at 1/1000, 1/60 and one second; for the one-second frame, place the camera on something.
2. At night or at dusk, from the side of a road, photograph the light trails of passing cars with a time of a few seconds, keeping the camera steady.
3. Photograph a cyclist or a runner passing in front of you at 1/30, turning the camera with them, at least ten times, and choose the best panning frame.
4. Photograph a friend standing still in front of flowing water with a long time, and look at whether their face stays sharp.

Check yourself

• Do the three water frames tell three separate feelings: frozen, softened, silky?
• In the panning frame, is the subject sharper than the background?
• In the long-time portrait, is the face sharp, and has the skin, whether dark or light, been recorded without its bright areas overflowing?

Glossary

Mini quiz

1. Which time is better suited to freezing a bird flapping its wings?

• A) 1/30
• B) A time of around a thousandth of a second or shorter
• C) Two seconds
• D) 1/15

2. Of two subjects moving at the same speed, which one blurs faster?

• A) The one crossing from one edge of the frame to the other
• B) The one walking toward the camera
• C) The one moving away from the camera
• D) Both blur in the same way

3. Why does the background flow in panning?

• A) Because the aperture is too wide
• B) Because ISO is too high
• C) Because as the camera turns with the subject, the still background slides across the sensor
• D) Because the photo was blurred afterward

4. In dim light, where should the light come from to freeze the face of a dark-skinned person?

• A) By lengthening the shutter speed to one second
• B) By shaking the camera
• C) By brightening the photo afterward
• D) By opening up the aperture or raising ISO, keeping the time short

Answers

1. B — A bird flapping its wings is very fast; for the wing not to leave a trace on the sensor, the shutter shouldn't stay open longer than a thousandth of a second.
2. A — A subject crossing sideways travels a long way across the sensor; a subject moving toward or away from the camera changes position little in the frame.
3. C — As the camera follows the subject, the subject stays in the same place on the sensor, while the still background slides and turns into horizontal lines.
4. D — A long time blurs the face; taking the light from the aperture or ISO keeps the time short enough to freeze.

Summary card

• A short time freezes the moment, a long time lets time flow.
• Freezing: walking ~1/250, running ~1/500–1/1000, drops and wings 1/1000+.
• A subject crossing sideways blurs quickly; one coming toward the camera more slowly.
• To let things flow the camera stays still; to pan the camera turns with the subject.
• In a long time, people shouldn't move; in dim light, take the light to freeze a face from the aperture or ISO.

Bridge to the next lesson

In this lesson we suggested taking the light to freeze faces not from the time but from the aperture or ISO. You know the aperture; but what is ISO, and why do photos come out grainy in the dark? The next lesson takes up the third corner of the exposure triangle: the setting that strengthens the sensor's signal and, as it rises, also makes grain grow.