S mode

Learning goal

You will be able to explain how movement stays in your control when you choose the shutter speed in S mode and leave the aperture to the camera. You will choose the time according to the subject's speed, watch the aperture the camera sets and the slice of sharpness that changes with it, understand why the photo darkens when the lens hits its widest opening and fix it with ISO, notice when the aperture hits its narrowest limit at long times, know that compensation changes the aperture and the sharpness in S mode, and catch faces of every tone sharp and correctly exposed on moving people.

The question

At a school fair, you are photographing your child's running race. As your child runs toward the finish line you press the shutter button, and in the photo there is only a colorful blur: legs, arms and face have melted into the movement. The camera was in full auto; it set the brightness correctly, but it didn't know the moment was a race.

When does S mode save the day? In every moment where movement is the subject of the photo. A ring of circle dancers, a dog chasing a ball, a gull flapping its wings, a spinning dancer, or the flow of a waterfall. In these moments the most important decision is the time itself, and in S mode you make that decision. In this lesson we will talk about how S mode works, at what point it parts from A mode, and in which situations it can surprise you.

Context

On the staircase we drew in Lesson 3.9, we defined S mode, that is shutter priority, as the step where you choose the time and the camera chooses the aperture; on some brands this mode is written with the letters Tv. In the previous lesson you saw the reverse division of labor in A mode: you chose the sharpness and the camera set the time. In S mode the roles swap and the priority passes to movement.

In Lesson 8.5 you saw that freezing and letting things flow is a storytelling decision, and roughly what time freezes each kind of movement. S mode is the easiest way to lock that decision at the moment of shooting. You choose a time, for example 1/1000; as the light changes the camera opens or closes the aperture, and your time stays in place. But when the aperture changes, the slice of sharpness changes too; that is why in S mode the display you need to watch is, this time, the aperture readout.

Simple explanation

How is the work shared in S mode?

In S mode the time is in your hands. The camera measures the scene and sets the aperture to reach a suitable brightness at the time you chose. If you shorten the time one stop, the camera opens the aperture one stop; if you lengthen it, it stops down. ISO can stay fixed or be automatic; that is your choice too. That way, whatever the light, movement freezes or flows as you want.

This mode is useful in every situation where movement is decisive. In sport and play, with running children and animals, flying birds, dance, and moments such as the circle dances at weddings, you freeze movement by keeping the time short. For panning you can fix the time at around 1/30, and on a tripod you can let a stream flow with half a second. One detail not to forget: in S mode the aperture the camera chooses changes from scene to scene. An aperture stopped down to f/11 in a bright moment can open up to f/4 in shade; this means the background looks sharp in one frame and soft in another. In group photos or frames where sharpness matters, you need to keep an eye on this change.

Where does S mode get stuck in dim light?

In A mode the danger in dim light was the time; in S mode the danger is the aperture. As the light falls, the camera opens the aperture: f/8, f/5.6, f/4. But every lens has a maximum aperture, the widest it can open; on many zoom lenses this value is around f/4, and on bright lenses between f/1.8 and f/2.8. When the camera hits this limit it can't open any further, and if there isn't enough light for the time you chose, the photo comes out dark. Many cameras warn you in this situation by blinking the aperture display.

The solution is usually in ISO. If you chose the time to freeze movement, you don't want to lengthen it; you make up the missing light by raising ISO. Auto ISO helps a lot here: you set the time, and the camera adjusts first the aperture and, if that isn't enough, ISO. When you want to freeze running children at 1/500 in an indoor sports hall, the lens's widest opening isn't enough, and ISO can go up to 3200 or higher. The conclusion from the ISO lesson holds here too: a slightly grainy but sharp frame is often more valuable than a blurred or dark one.

What happens in bright light and at long times?

The opposite can happen too. When you set the time to half a second to let a waterfall flow in daylight, the camera stops the aperture down as far as it can to balance such a long time. A lens's minimum aperture, its narrowest opening, is often around f/16 or f/22; when the camera hits this limit it can't stop down any further and the photo is overexposed. What's more, at openings this narrow, diffraction softens the whole photo slightly.

In a moment like this, pulling ISO to its lowest gains a few clicks. Moving into shade, waiting for the evening hours, or using the light-cutting filters you will see later are the real solutions. The same problem can come up when panning on a bright day: a time of 1/30 gathers too much light in the sun and the camera stops the aperture down to its narrowest. In S mode, looking at the aperture value on the display lets you notice at the moment of shooting that you have hit these limits. If the warning is blinking, it is you, not the camera, who must rescue the brightness.

How do compensation and skin work in S mode?

When you change exposure compensation in S mode, the time stays in place and the camera changes the aperture. This is how exposure compensation (shutter priority) works: +1 EV compensation opens the aperture one stop, −1 EV stops it down one stop. This lets you adjust brightness without spoiling the movement; but the slice of sharpness changes along with the compensation. The crowd behind a runner can soften a little more with plus compensation. If compensation pushes the aperture to the lens's limit, the photo doesn't brighten as much as you expect; then you need to raise ISO as well.

In moving scenes, the point to watch for skin tone is that a fast time gathers little light. When you photograph a dark-skinned child running on a sunny beach or in front of a bright sky in S mode, the meter finds the bright background too much and stops the aperture down; the face stays in darkness. Plus compensation brightens the face by opening the aperture. When photographing a light-skinned athlete in front of a dark floor in an indoor hall, on the other hand, the meter can make the face glow too much; minus compensation balances this. In every case, looking at the screen to see whether the face is correctly exposed, without changing the time, is the way to freeze movement without losing the skin.

Visual evidence

At a school fair, you photograph the running race with the camera in S mode at 1/1000. In the sunny schoolyard the camera sets the aperture to f/5.6. The running children are frozen in the air; a foot has left the ground, hair hangs in the wind, and the effort and laughter on their faces are sharp. A cloud passes in front of the sun; the camera opens the aperture to f/4 and the parents behind soften a little more, but the children are still frozen.

The races move into the indoor sports hall. You want to photograph the relay race at 1/500; the lens's widest opening is f/4, the aperture display is blinking, and the first frames are dark. You turn on auto ISO, the camera raises ISO to 3200 and the frames brighten; there is a fine grain, but the running children are sharp. Finally a dark-skinned girl takes the baton and runs with the bright windows of the hall behind her; her face is dark. You move compensation two thirds of a stop into the plus side, the camera raises ISO a little more, and the girl's face brightens with her tightly closed lips and the drops of sweat on her forehead. The same time, three different lights; each time, an eye watching what was changing saved the photo.

Common mistakes

Summary

S mode gives movement to the photographer and the aperture to the camera: the time stays fixed, the opening shifts as the light changes, and the slice of sharpness changes along with it. This division of labor has two ends; in dim light the lens can't open any further and the frame darkens, and at long times it can't stop down any further and the frame blows out. Watching the aperture display and making up the missing light with ISO, taking into account that compensation in S mode shifts the opening and the sharpness, and adjusting faces of every tone running in front of a bright window or a dark floor with compensation keeps the skin and the exposure while freezing movement.

Mini assignment

In this assignment you will shoot only in S mode in a place where movement is the subject.

1. In a park, a playground or at a match, photograph moving people at 1/500 and 1/1000 and note the apertures the camera chooses.
2. Photograph the same subjects in shade or indoors; when the aperture display starts to blink, leave ISO on auto or raise it by hand.
3. Photograph flowing water or a passing cyclist at 1/15 or 1/30 and see whether the camera hits the narrowest opening.
4. Photograph someone moving in front of a bright background, expose the face correctly with compensation if needed, and note how the compensation changed the aperture.

Check yourself

• Did the moving subjects really freeze at the times you chose?
• Were you able to notice during the shoot the moments when the aperture display was blinking?
• In the moving frames, are faces, whatever their skin tone, sharp and correctly exposed?

Glossary

Mini quiz

1. When you shorten the time one stop in S mode, what does the camera do?

• A) It warms the white balance
• B) It lengthens the time back
• C) It opens the aperture one stop
• D) It refocuses

2. If frames taken at 1/500 in S mode in an indoor hall are dark and the aperture display is blinking, what is the reason?

• A) The camera has hit the lens's widest opening and can't open any further
• B) The time is too long
• C) The white balance is wrong
• D) The aperture is too open

3. In S mode, what is the best way to make up missing light while keeping the movement?

• A) Lengthening the time
• B) Raising ISO
• C) Stopping the aperture down
• D) Brightening the photo afterward

4. If the face of a dark-skinned child running on a bright beach comes out dark in S mode, what do you do?

• A) Lengthen the time to 1/30
• B) Switch the camera to A mode
• C) Pull ISO to its lowest
• D) Give plus compensation; the camera keeps the time and opens the aperture

Answers

1. C — A shortened time halves the light; the camera balances it by opening the aperture one stop to keep the brightness.
2. A — Every lens has a limit to how wide it can open; when the camera hits it, it can't gather enough light for the chosen time.
3. B — Because the time decides the movement, it is kept; the missing light is made up with ISO, and a little grain is better than a blurred frame.
4. D — The meter finds the bright sand too much and stops the aperture down; plus compensation brightens the face by opening the aperture without changing the time.

Summary card

• S mode: the time is yours, the aperture the camera's.
• If movement is the subject, fix the time; let the camera meet changes in light with the aperture.
• Watch the aperture display: in dim light it hits the widest opening, at long times the narrowest.
• Keep the time; make up the missing light with ISO.
• Compensation in S mode changes the aperture and the sharpness; expose a moving face correctly with compensation.

Bridge to the next lesson

In A mode you chose sharpness, in S mode movement, and left the rest to the camera. But what if you want to choose all three settings yourself at the same time? Many people think manual mode is a hard area that belongs only to experts. The next lesson shows that manual mode isn't as hard as it seems, and how auto ISO turns it into a safe middle path.