A mode

Learning goal

You will be able to explain what is your decision and what is the camera's when you choose the aperture in A mode and leave the shutter speed to the camera. You will choose the aperture according to the scene's need for sharpness, glance at the shutter speed the camera works out in every shot, notice when the time drops below the safe limit in dim light and fix it with ISO, understand when the camera hits its shortest time in bright sun and stop the aperture down, know that exposure compensation changes only the shutter speed in A mode, and expose different skins correctly in front of bright or dark backgrounds with compensation.

The question

If you look at the cameras of experienced photographers shooting a wedding, a street walk or a family meal, you will see that the mode dial is often on the letter A. Not in full auto, and not in full manual either. Somewhere in between: they choose one setting themselves and leave the rest to the camera.

Why do professionals love A mode? Because they can keep in their own hands one of the decisions that most noticeably changes how a photo looks, the slice of sharpness, while leaving the calculation to the camera in moments when the light changes fast. In this lesson we will talk about how A mode works, why it is so useful, and in which situations it can let you down.

Context

In Lesson 3.9 we compared the shooting modes to a staircase and defined A mode, that is aperture priority, as the mode where you choose the aperture and the camera chooses the shutter speed. On some brands the same mode is written with the letters Av. That day you knew what this mode did; but you didn't yet know how the aperture, shutter speed and ISO balance each other. Now you know the exposure triangle and stops; you can see what A mode does behind the scenes.

Remember the priority question from Lesson 8.7: what you wanted to protect first in a scene decided which setting was chosen first. A mode is that decision handed over to the camera for scenes where the priority is sharpness: you choose the slice of sharpness with the aperture, and the camera works out the shutter speed to reach the brightness its light meter suggests. As the light changes, the shutter speed changes too; the aperture stays where you left it. That is why your real job in A mode is to watch the time the camera chooses.

Simple explanation

Who decides what in A mode?

In this mode your hand decides the opening. The camera measures the scene and works out the shutter speed needed to reach a suitable brightness at that aperture. As for ISO, you either fix it or leave it to the camera's own adjustment. When you open the aperture one stop, the camera shortens the shutter speed one stop; if you stop the aperture down, it lengthens the time. That way the brightness stays the same, but the slice of sharpness changes as you want.

The reason A mode appeals to professionals is that sharpness is the most eye-catching decision in most scenes. The background melting away in a portrait, everything being sharp from front to back in a landscape, everyone staying in focus in a group photo depend on the aperture. Light, on the other hand, changes all the time: a cloud passes, the subject steps into shade, you move from one room to another. In A mode the camera meets these changes with the shutter speed; you make the sharpness decision once and focus on the subject. As long as the shutter speed stays in a safe range, this division of labor works very well.

Why can A mode let you down in dim light?

The biggest trap of A mode is dim light. As the light falls, the camera lengthens the shutter speed to keep the brightness: 1/250, 1/60, 1/15, even longer. The camera looks only at brightness; it doesn't know whether your hand is shaking or whether the subject is moving. The result is a photo at the right brightness but blurred. That is why, when shooting in A mode, glancing at the shutter speed readout in the viewfinder or on the screen, the time the camera has chosen, is the most important habit.

If the time drops below the safe limit from Lesson 8.4, you can open the aperture a little more, raise ISO or rest the camera on a solid surface. On many cameras, when you leave ISO on auto, you can also set a minimum shutter speed setting; instead of letting the time fall below this limit, the camera raises ISO. The name and place of this setting change from camera to camera, but the safeguard it gives is the same. When photographing people, putting this limit at around 1/125 keeps moving faces sharp. We will look at auto ISO and this limit in more detail in the manual mode lesson.

Why does A mode blow out in bright sun?

In bright sun the opposite happens. When you open the aperture very wide for a portrait, for example to f/1.8, so much light reaches the sensor that the camera has to shorten the shutter speed a lot. Every camera has a maximum shutter speed, its shortest time; on most cameras, with the mechanical shutter, this is around 1/4000 or 1/8000. When the camera hits this limit, it can't shorten any further and the photo is overexposed. Many cameras warn you in this situation by blinking the shutter speed display.

If you see this warning, you have a few options. Lowering ISO to its base value can gain a stop or two. If your camera has an electronic shutter, it often allows shorter times. If these aren't enough, you need to stop the aperture down a little; even around f/3.5 instead of f/1.8 still softens the background. Moving into shade is a solution too. In bright sun, a white dress, the forehead of light skin or the sky are the first places to blow out when the camera's limit is hit; glancing at the shutter speed display catches these losses before the shot.

How does compensation work in A mode?

In A mode, the camera's light meter tries to pull the scene toward an average brightness and goes wrong in scenes such as snow, a beach or a dark background. This is where exposure compensation comes in. One important detail: exposure compensation in A mode leaves the aperture in place; the camera changes only the shutter speed. +1 EV compensation lengthens the time by one stop; −1 EV shortens it by one stop. That way you can adjust the brightness without spoiling your sharpness decision.

Skin tone turns into a measurable decision with this setting. When you photograph a dark-skinned person standing in front of a bright window or a white wall in A mode, the camera finds the brightness of the background too much, shortens the time and leaves the face in darkness. Moving compensation into the plus side, between two thirds of a stop and one stop, brings back the face's own color and texture. When you photograph a light-skinned person standing in front of a dark background, on the other hand, the camera lengthens the time to make up for the darkness, and the face glows too much; a few clicks of minus compensation take this glow back. After compensating, don't forget to check whether the camera's new shutter speed is still in a safe range.

Visual evidence

You are photographing portraits of the bride and groom at a country wedding, and the camera is in A mode. In the midday sun, next to a tree, you want to photograph the bride at f/1.8; ISO has been left at 400. The shutter speed display is blinking and the photo is pure white: the lace of the wedding dress and the bride's light-skinned forehead have blown out. You lower ISO to 100, gaining two stops; the display is still at the limit. You stop the aperture down to f/2.8. Now the texture of the dress can be made out, and the trees in the background are still soft.

In the late afternoon you move into the wedding hall. The aperture is still at f/2.8, but this time the camera has lengthened the shutter speed to 1/20; in the first frames the dancing couple's faces are blurred. You turn on auto ISO and limit the longest time to 1/125; the camera raises ISO and the faces sharpen. Finally you photograph the dark-skinned groom with a bright window behind him. His face has stayed in darkness; you move compensation one stop into the plus side. The aperture is still f/2.8, only the time lengthens, and the groom's face brightens with the lines of his smile and the texture of his tie. Three scenes, the same aperture; each time, an eye watching the time the camera chose saved the shot.

Common mistakes

Summary

In A mode you choose the aperture, that is the slice of sharpness; the camera measures the scene and works out the shutter speed to keep the brightness. This division of labor is very useful in moments when the light changes fast, but the camera looks only at brightness: in dim light it can lengthen the time unsafely, and in bright sun it can hit its shortest time and blow the photo out. Watching the shutter speed in every shot, adjusting ISO and the time limit when needed, and knowing that compensation changes only the time in A mode while exposing different skins correctly in front of bright or dark backgrounds with compensation, makes this mode reliable.

Mini assignment

In this assignment you will shoot only in A mode for a whole day.

1. Choose a wide aperture for a portrait and a medium one for a landscape or a group, and note the shutter speed the camera chooses in every frame.
2. When you go indoors or evening comes, find where the time drops below the safe limit, and fix it with ISO or the longest time limit.
3. In the midday sun, take a frame at the lens's widest value and check whether the camera gives a warning; if needed, lower ISO or stop the aperture down.
4. Photograph a dark-skinned person in front of a bright background and a light-skinned person in front of a dark background, and note in stops the compensation each one needed.

Check yourself

• Can you say in what range the times the camera chose wandered through the day?
• Were you able to catch and fix a blurred or blown-out frame at the moment of shooting?
• After compensating, did the skin of both faces separate from the background and reach its natural color?

Glossary

Mini quiz

1. When you open the aperture one stop in A mode, what does the camera do?

• A) It raises ISO one stop
• B) It shortens the shutter speed one stop
• C) It stops the aperture back down
• D) It refocuses

2. If photos taken in A mode in a dim hall are at the right brightness but blurred, what is the cause?

• A) The camera lengthening the shutter speed unsafely to keep the brightness
• B) The aperture being too narrow
• C) The white balance being wrong
• D) ISO being too high

3. If the shutter speed display is blinking at f/1.8 in bright sun, what has happened?

• A) The camera has broken down
• B) The photo will come out too dark
• C) The aperture has stopped itself down
• D) The camera has hit its shortest time and the photo will be overexposed

4. If a dark-skinned face in front of a bright window comes out dark in A mode, what do you do?

• A) Stop the aperture down to its narrowest
• B) Give minus compensation
• C) Give plus compensation; the camera lengthens the time without changing the aperture
• D) Change the white balance

Answers

1. B — The opened aperture brings twice the light; the camera halves the time to stay at the same brightness.
2. A — The camera looks only at brightness; in dim light it lengthens the time, and hand shake or subject movement blurs the photo.
3. D — Because the camera can't give a shorter time, it can't balance the extra light; the blinking display is an overexposure warning.
4. C — The meter finds the bright background too much and darkens the face; plus compensation in A mode brings the face to the right brightness by lengthening only the time.

Summary card

• A mode: the aperture is yours, the shutter speed the camera's.
• Make the sharpness decision once; let the camera meet the change in light.
• Glance at the shutter speed in every frame: it lengthens in dim light, hits the limit in sun.
• In dim light, ISO or a longest time limit; in sun, a low ISO or a slightly narrower aperture.
• Compensation in A mode changes only the time; expose a face in front of a background correctly with compensation.

Bridge to the next lesson

In A mode your priority was sharpness; you left the shutter speed to the camera and watched it. But in some moments the priority turns around: a running child, an athlete leaping into the air, or a passing train. Then you choose the time and leave the aperture to the camera. The next lesson explains this reverse division of labor, and the moments when S mode saves the day.