Aperture priority is the camera mode where you choose the aperture and the camera chooses the shutter speed that gives a correct exposure. It matters because aperture decides how much of the picture is sharp, from one petal to a whole valley, and this mode lets you make that choice while the camera keeps up with the changing light.
It is marked A or Av on the mode dial, depending on the camera. Both mean the same thing. The rest of this page explains what the camera is doing behind your back in this mode, where it gets things wrong, and how to take back control at exactly those moments.
What you set, what the camera sets
An exposure has three settings: aperture, shutter speed and ISO. In aperture priority you turn a dial to pick the f-number. The camera’s meter measures the scene and sets the shutter speed to match. If ISO is fixed, that is the whole deal: your aperture, the camera’s shutter. If Auto ISO is on, the camera also gets to move ISO, which changes the picture in ways covered further down.
The key thing to understand: changing the aperture in this mode does not change how bright the photo is. Open up one stop and the lens lets in twice the light, so the camera halves the shutter time. Close down one stop and the camera doubles it. The brightness stays put. What changes is the look of the picture: how deep the sharp zone is, and whether the shutter is fast enough to freeze movement.
Here is one scene, metered at ISO 100 on a bright overcast day, as you turn the aperture dial. Every row is the same exposure.
| You set | Camera picks | Depth of field | What to watch |
|---|---|---|---|
| f/2.8 | 1/1000 | Very shallow | Missed focus shows easily |
| f/4 | 1/500 | Shallow | Freezes most walking and running |
| f/5.6 | 1/250 | Moderate | Safe handheld with most lenses |
| f/8 | 1/125 | Deep | Fine for still subjects |
| f/11 | 1/60 | Deeper | Hand shake starts to matter with longer lenses |
| f/16 | 1/30 | Very deep | Shake and moving subjects blur; diffraction softens detail |
| f/22 | 1/15 | Deepest | Tripod territory; diffraction is clearly visible |
Each row is one stop from the next, so each shutter speed is half or double its neighbor. The camera does this arithmetic for you in real time. If you want to see the same trade with every setting free to move, the exposure triangle page has an interactive that locks the exposure while you pick which setting pays.
Read the table from the bottom up and you see the hidden cost of a small aperture. f/16 does not only make the background sharp. It also hands you a shutter speed that is sixteen times slower than f/4, and in dimmer light that is often slow enough to blur the whole photo.
Try it in the camera simulator: switch to Aperture priority, open up to f/2.8 or wider, focus on the subject, and watch which shutter speed the camera chooses to keep the exposure right.
Choosing the aperture: three starting points
The aperture you pick depends on what you want sharp. These are starting points, not rules, and the depth of field calculator shows exactly how far the sharp zone reaches for your lens and distance.
Wide open, about f/1.8 to f/4, to isolate one thing. A face, a flower, a cup on a table. The background melts into blur and the subject stands alone. This is where shallow depth of field lives. The lace flower at the top of this page was shot at f/2.8 with an 80mm lens, and the leaves behind it are just soft shapes. Focus has to be exact here, because the sharp zone can be a few centimeters deep at close range.
The middle, about f/5.6 to f/8, for people in places and quick moments. Enough depth that a person and their surroundings both read clearly, and enough slack that focus does not have to be perfect. Most lenses are at or near their sharpest here, a range often called the lens’s sweet spot.
Small, about f/8 to f/11, for scenes that should be sharp from front to back. Landscapes and architecture. Combine it with careful focus placement, explained on the hyperfocal distance page, and the sharp zone can run from a few meters away to the horizon. The sandstone photo above was made at f/11, with the scrub in front and the far rock both holding detail.
Going smaller than f/11 is a trade, not a free upgrade. At f/16 and f/22 light spreads as it passes through the tiny opening, and diffraction softens fine detail across the whole frame. You gain depth and lose crispness. Use f/16 when you truly need the depth, not as a default for “sharp”.
To see what each starting point does, set an aperture in the tool below, focus on one of the figures, and watch how far in front of it and behind it things stay sharp.
Not sure why a bigger number means a smaller hole? The f-stop page explains the scale and why each full stop is a factor of about 1.4.
Zoom first, then set the aperture
Many zoom lenses have a widest aperture that changes as you zoom, for example f/3.5 at the wide end and f/5.6 at the long end. Set f/3.5 at the wide end, zoom in, and the camera quietly moves you to f/5.6, with a slower shutter to match. Frame the shot first, then check the aperture. The variable aperture page explains why the lens does this.
How the camera decides as the light falls
This is the part most guides leave out, and it is the part that explains most blurry photos taken in aperture priority. With Auto ISO switched on, the camera follows a fixed order of decisions as the light drops. Knowing that order means you can predict what it will do before you press the shutter.
Say you have set f/4, Auto ISO from 100 to 6400, and a minimum shutter speed of 1/125. Light is measured in exposure value (EV), where each step down is half the light. Here is what the camera chooses:
| Light (EV at ISO 100) | Typical scene | Shutter | ISO | What is happening |
|---|---|---|---|---|
| 15 | Bright sun | 1/2000 | 100 | Plenty of light, very fast shutter |
| 13 | Bright overcast | 1/500 | 100 | Shutter slows as light falls |
| 11 | Dull day, deep shade | 1/125 | 100 | Shutter reaches your minimum |
| 10 | Fading daylight | 1/125 | 200 | Shutter holds; ISO starts to climb |
| 8 | Bright interior | 1/125 | 800 | ISO keeps climbing |
| 6 | Ordinary room at home | 1/125 | 3200 | Noise starts to show, more so on small sensors |
| 5 | Dim room | 1/125 | 6400 | ISO hits your ceiling |
| 4 | Very dim room | 1/60 | 6400 | Shutter drops below your minimum |
| 3 | Near dark | 1/30 | 6400 | Blur from shake and movement is likely |
Three phases: first the shutter slows to your floor, then ISO climbs to your ceiling, then the shutter falls below the floor because there is nothing else left to give. That last phase is the trap. The camera will not refuse to take the picture. It will simply pick 1/30 and let you find the blur later. When the shutter reading drops below your minimum, it is time to open the aperture, raise the ISO ceiling, add light or brace the camera.
Your camera’s exact steps may differ slightly, and some cameras pick the minimum shutter speed automatically from the focal length, but the order is the same. Set up the limits once on the Auto ISO menu and this ladder runs every time you shoot.
With ISO fixed instead of Auto, the ladder is simpler and harsher: only the shutter moves. At f/16 and ISO 100 in a dim room around EV 5, the camera picks 8 seconds. Even at ISO 3200 it would still be 1/4 second.
Wide open is also the fast shutter setting
Because the camera always balances the exposure, the widest aperture your lens allows also gives the fastest shutter speed the light allows. That makes aperture priority a good action mode in dim light: open the lens all the way and the camera will automatically use the quickest shutter it can. The gulls above show what happens when the shutter is left too slow. At 200mm, f/6.3 and ISO 200 in late light, the camera chose 1/160, and the flapping wings smeared. An f/4 lens would have let in about 1.3 stops more light, so the same scene would meter at about 1/400. Raise ISO to 500 as well and you reach 1/1000, fast enough to freeze most of the flock. Pair this with an Auto ISO minimum of about 1/500 or 1/1000 for moving subjects, as the freezing motion page explains.
What “fast enough” means for your minimum shutter
A common starting point for handheld shots is one over the focal length: 1/50 for a 50mm lens, 1/200 for a 200mm lens. On a crop sensor, multiply the focal length by the crop factor first, so a 50mm lens on a 1.5x sensor wants about 1/75, which you round to the next setting, 1/80. Image stabilization lets you go several stops slower for a still subject, but it does nothing for a subject that moves. A person walking needs about 1/125 to 1/250 to look sharp whatever the lens. The camera shake page shows how to tell shake blur from subject blur.
When the camera runs out of shutter speeds
Aperture priority works only while the camera has a shutter speed left to give. At either end it can run out, and many cameras warn you by blinking the shutter speed in the viewfinder.
Too much light. At f/1.4, ISO 100, in bright sun around EV 15, a correct exposure needs about 1/16000. Many cameras top out at 1/4000 or 1/8000 with the mechanical shutter, so the photo comes out one to two stops too bright. Close down to f/2.8 (about 1/4000), switch to the electronic shutter if your camera has one, or use an ND filter to keep the wide aperture.
Too little light. Most cameras will not go longer than 30 seconds in aperture priority. If the meter wants longer, the photo comes out too dark. Raise the ISO, open the aperture, or switch to manual mode and use Bulb.
Long exposures of water show both sides of this. The creek above was a 240 second exposure at f/11, far beyond the 30 second ceiling, so it had to be made in manual or Bulb. But aperture priority still has a place with smooth water. Put a 10-stop ND filter on a lens at f/11 and ISO 100 on an overcast day: without the filter the meter reads about 1/60, with it about 15 seconds. That fits inside 30 seconds, so the camera can work it out for you. The waterfall page has the rest of the method.
When the meter is fooled, and how to correct it
The camera’s meter does not know what it is looking at. It assumes the scene averages out to middle gray and sets the shutter speed to make it so. Most scenes are close enough. Some are not.
A field of snow, like the one in front of this red barn, is much brighter than middle gray. Left alone, the meter tries to pull it down, so the snow comes out a dull gray and the barn too dark. A black dog on dark wood fools it the other way, and the result is washed out. A person with a bright window behind them comes out as a silhouette, because the meter is mostly reading the window.
The fix in aperture priority is exposure compensation, the plus and minus dial. Plus one tells the camera to give one stop more light than the meter suggests. Start at about +1 for a frame full of snow or white sand, about -1 for a dark scene that should stay dark, then take a test shot and check the histogram rather than the screen, which is often too bright to judge outdoors.
How the camera delivers the extra light depends on where it is on the ladder above. With ISO fixed, compensation always changes the shutter speed. With Auto ISO, it may change the ISO instead, or both. If you are already at your shutter floor, +1 usually means double the ISO, not half the shutter speed. Your aperture never changes, because that is the one setting you told the camera to leave alone.
Want to practice this without a camera? The camera simulator has an Aperture mode with exposure compensation, and a Snow scene where the meter gets it wrong until you add some.
Lock the exposure before you recompose
The meter takes a fresh reading every time you move the camera. Meter on a face, swing the camera to put the face off to one side, and if a bright sky slides into the frame the exposure changes with it. Point the camera at what matters, press the AE lock button to hold that reading, then recompose and shoot. For a small subject in strong backlight, switching to spot metering does a similar job: the camera exposes for the spot under the focus point and ignores the window.
Wondering which metering mode your camera is using right now, and what each one looks at? Metering modes compares them on real photos.
Depth of field preview
Most viewfinders show you the scene with the lens wide open, because that gives the brightest view. So at f/11 you may see a blurred background that will be sharp in the photo. Many cameras have a depth of field preview button that closes the lens to your chosen aperture so you can see the real depth. The view gets darker, which is normal. Some electronic viewfinders can be set to show the working aperture all the time.
Aperture priority, shutter priority or manual?
Each mode divides the work differently. None is more serious than another. The camera modes page covers all of them; this is how aperture priority sits among them.
- Aperture priority when the look of the depth is what matters and the light keeps changing: people, travel, street, landscapes in moving cloud, and action in dim light with the lens wide open.
- Shutter priority when one exact shutter speed matters more than anything: panning at 1/30, freezing a ball at 1/2000, or blurring a stream by hand at 1/4. You choose the motion; the camera chooses the aperture, and depth goes wherever it goes.
- Manual when the light is steady and you want every frame identical: a panorama sequence whose frames must match, studio flash, a stage where spotlights swing the meter wildly, or anything longer than 30 seconds. Manual with Auto ISO is a common hybrid: you set aperture and shutter, the camera sets ISO.
The practical test: if you keep fighting the camera with exposure compensation and every frame comes out different, the light is steady enough for manual. If you keep resetting the shutter speed by hand as clouds pass, aperture priority will do that work for you.
Flash in aperture priority
With flash in aperture priority, the camera still sets the shutter for the background light, and the flash lights the subject. In daylight that is limited by the flash sync speed, often about 1/200, and the camera will not set a faster shutter than that, so a wide aperture in bright sun can overexpose the background. At night, depending on the camera’s settings, it may choose a slow shutter so the background registers, which looks good but needs a steady camera. The flash and ambient light page explains how to balance the two.
Want to check you know which mode to reach for? Try the camera modes quiz.
Common mistakes with aperture priority
Not watching the shutter speed. The camera never refuses a slow shutter. Glance at the number before every shot in changing light, and if it is lower than one over your focal length, or lower than the subject’s movement allows, open up or raise the ISO.
Thinking the aperture dial makes the photo brighter. In this mode it does not. If photos are too bright or too dark, the answer is exposure compensation, not a different aperture.
Using f/16 or f/22 “to be safe”. More depth than you need costs shutter speed and sharpness. f/8 to f/11 is often sharper overall than f/22, even for landscapes.
Always shooting wide open. Most lenses are a little softer at their widest aperture, and the sharp zone may be thinner than your subject. Closing down one stop, say f/1.8 to f/2.8, often gives a crisper subject and still a soft background.
Using Auto ISO with no limits. Without a minimum shutter speed the camera may hold ISO 100 and drop to 1/15. Without a ceiling it may push ISO beyond what your camera handles well. Set both.
Trusting the viewfinder to show depth. It usually shows the lens wide open. Use depth of field preview or zoom into the photo afterward.
Try this: one subject, five apertures, one exposure
This takes ten minutes and shows the whole mode working. You need a camera with an A or Av mode. Most phone cameras have a fixed aperture, so a phone cannot do this one.
- Put something small, like a mug, on a table about a meter from you, with something busy a few meters behind it: a shelf, a garden, a window.
- Set aperture priority, ISO fixed at 100 or 200, and exposure compensation at zero.
- Focus on the mug and shoot at your widest aperture, then f/4, f/5.6, f/8, f/11 and f/16. Do not move.
- Write down the shutter speed the camera chose for each frame.
- Now fill the frame with a white wall or a sheet of white paper, and shoot it at 0, then at +1.
How to judge it. The five mug shots should all look about equally bright; if they do, you have seen the camera trade shutter for aperture. From f/4 onward, each shutter speed should be close to double the one before, because each step is one stop smaller. Look at the background: find the frame where it stops being a blur and starts being a place, and note the aperture. That is your own feel for depth on that lens. Then check the slowest frames at full size: any doubling or smear is shake, and it tells you your real handheld limit. Finally, compare the two white shots. The 0 frame will look grayish, and the +1 frame closer to white.
Seen the background change and want to know how far the sharp zone reaches before you shoot? The depth of field page explains the four things that control it.
Questions people ask about aperture priority
What is the difference between A and Av on the dial?
Nothing but the label. Av stands for aperture value and A for aperture; both let you set the aperture while the camera sets the shutter speed.
Why are my aperture priority photos blurry indoors?
The camera picked a shutter speed too slow to hold by hand, often because the aperture was small or the ISO fixed and low. Check the shutter reading, open the aperture, and set Auto ISO with a minimum shutter speed so the camera raises ISO before it slows down.
Does exposure compensation change the aperture?
Never in aperture priority. It changes the shutter speed, or with Auto ISO on, it may change the ISO instead. The aperture stays where you put it.
Can I use aperture priority for sports or wildlife?
Yes. Open the lens wide, turn on Auto ISO, and set the minimum shutter speed to suit the action, about 1/500 to 1/2000. The camera then raises ISO to protect that speed. Shutter priority does the same job, but leaves the aperture, and so the depth, to the camera.
Why does my shutter speed blink?
The camera has run out of shutter speeds for that aperture and ISO. If the slowest speed blinks the photo will be too dark: open the aperture or raise ISO. If the fastest speed blinks it will be too bright: close the aperture, lower ISO or use an ND filter.
Is aperture priority cheating compared with manual?
No. You still make the creative choice, the depth, and you still correct the meter with compensation. Manual earns its place when the light is steady or the meter is unreliable, not because it is more serious.