To stop down is to close your lens’s aperture to a smaller opening, which means a higher f-number: going from f/2.8 to f/8 is stopping down three stops. It matters because that one turn of a dial changes three things at once: how much light reaches the sensor, how much of the scene is sharp from near to far, and how sharp the lens itself draws.
This page is about stopping down as an action you take: what the phrase means when photographers use it, what each stop costs and buys, how far to go for the picture in front of you, why your viewfinder does not show the result, and when not to do it at all.
What “stopping down” means, and what “stopped down” is measured from
The aperture is the adjustable opening inside the lens. Stopping down makes it smaller; the opposite, making it larger, is called opening up. A lens set to its largest opening is “wide open”. Anything smaller is “stopped down”.
When someone says a lens was “stopped down two stops”, they mean two stops smaller than that lens’s widest setting, so the f-number it ends up at depends on the lens:
| Lens’s widest aperture | Stopped down 1 stop | Stopped down 2 stops | Stopped down 3 stops |
|---|---|---|---|
| f/1.4 | f/2 | f/2.8 | f/4 |
| f/2.8 | f/4 | f/5.6 | f/8 |
| f/4 | f/5.6 | f/8 | f/11 |
That is why lens reviews say things like “sharp across the frame once stopped down a stop”: the advice is about where that lens sits relative to its own maximum, not about one f-number for every lens. On a zoom whose widest aperture changes as you zoom, such as an f/3.5 to 5.6 lens, zooming in narrows the widest setting by itself; variable aperture lenses covers what that does to your exposure.
The word “stop” came from the brass plates with holes of different sizes that early photographers slid into the lens to stop down the light. Today it means any doubling or halving of light, on any control, so you will also hear “stop down” used loosely for making an exposure one stop darker in general.
Want the unit itself, and how a stop on the aperture trades against a stop of shutter speed or ISO? Stops in photography counts them on every control.
The arithmetic of one stop down
The f-number is the lens’s focal length divided by the diameter of its opening. A 50mm lens at f/2 has an opening 25mm across; at f/8 it is 6.25mm across. To halve the light you halve the area of the opening, which means dividing its diameter by the square root of 2, about 1.4. So each full stop down multiplies the f-number by about 1.4, which gives the familiar sequence:
f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
Every step to the right lets in half the light of the one before it. Two steps is a quarter, three steps an eighth. Doubling the f-number, f/4 to f/8 for example, is always two stops.
Most cameras move the aperture in thirds of a stop, so the dial clicks f/2.8, f/3.2, f/3.5, f/4, f/4.5, f/5, f/5.6, f/6.3, f/7.1, f/8, f/9, f/10, f/11. Three clicks is one stop. Counting clicks is the quickest way to know how far you have stopped down without doing any arithmetic. The f-stop scale page explains why the numbers run the way they do.
What changes when you stop down
Exposure: half the light per stop
Each stop down halves the light, so something else has to give if the picture is to stay as bright. In aperture priority the camera does it for you by doubling the shutter time. In manual you do it yourself: one stop longer on the shutter speed, or one stop higher on the ISO, for every stop you close. That is the whole trade in the exposure triangle, and it is the main cost of stopping down.
Depth of field: more of the scene is sharp
A smaller opening sends narrower cones of light to the sensor, so points in front of and behind the focus distance blur less. More of the scene looks sharp. The table shows how fast that zone grows for one real case: a 50mm lens on a full frame camera focused on a subject 3 m away, with the usual 0.03 mm circle of confusion.
| Aperture | Sharp from | Sharp to | Depth of field |
|---|---|---|---|
| f/2.8 | 2.73 m | 3.33 m | 0.60 m |
| f/4 | 2.63 m | 3.49 m | 0.87 m |
| f/5.6 | 2.50 m | 3.74 m | 1.24 m |
| f/8 | 2.34 m | 4.19 m | 1.85 m |
| f/11 | 2.16 m | 4.91 m | 2.75 m |
| f/16 | 1.92 m | 6.92 m | 5.00 m |
| f/22 | 1.69 m | 13.56 m | 11.88 m |
Two things stand out. Each stop adds roughly 40 to 50 percent more depth at first, then the far limit runs away quickly as you approach the hyperfocal distance. And the zone always grows more behind the subject than in front of it. The depth of field page covers the other three controls that move this zone: focal length, focus distance and sensor size.
Change the aperture in the tool below and watch which figures in the row come into focus as you stop down, and how much of that depends on focal length and distance as well.
Lens sharpness: better, then worse
Almost every lens is a little soft wide open, especially toward the corners, because the outer parts of the glass bend light less precisely. Stopping down blocks those outer rays, so sharpness and contrast climb for the first stop or two. Keep going, though, and diffraction takes over: light spreading at the edge of a small hole blurs every point a little, and the blur grows with the f-number. That rise and fall gives each lens a sweet spot, usually two or three stops below wide open.
Corners, highlights and sunstars
Stopping down one or two stops also evens out vignetting, the darkening toward the corners that most lenses show wide open. Out of focus highlights change shape on many lenses: round wide open, they start to take the polygon shape of the aperture blades a stop or two down, which changes the look of the bokeh. And small bright lights, such as the sun peeking past a branch or street lamps at night, turn into points of light with rays. At f/11 to f/16 those rays are crisp; shooting a star-shaped lens flare covers how the number of blades sets the number of points.
How far to stop down for the picture you want
There is no single right amount. Decide what you are stopping down for, then stop when you have it:
- For the lens’s best sharpness: two or three stops below wide open, often f/5.6 to f/8 on a full frame camera. Going further adds depth but costs fine detail.
- For depth, front to back: only as far as the nearest and farthest things you care about need. Work it out with a depth of field calculator, or focus at the hyperfocal distance, before reaching for f/22.
- For sunstars: f/11 to f/16, accepting a little softness for the rays.
- For less light: stopping down works, but it also adds depth. If you want a slow shutter and a shallow focus, or the light is still too strong at f/16, use an ND filter instead.
- For a close-up: stop down to f/8 to f/11 and accept that it will not be enough on its own; at high magnification even f/16 gives only millimeters of depth, which is why close-up photographers turn to focus stacking.
Wondering exactly where your own lens peaks and fades? Finding your lens’s sweet spot walks through a test, and diffraction in photography shows why small apertures soften and when it starts to show.
How small is too small
Diffraction spreads a point of light into a spot about 2.44 times the wavelength times the f-number. For green light (0.00055 mm) that spot is about 0.011 mm across at f/8, 0.015 mm at f/11, 0.021 mm at f/16 and 0.030 mm at f/22. A modern full frame sensor has pixels only 4 to 6 thousandths of a millimeter wide, so at 100 percent you start to see the softening around f/11. At f/22 the spot is as large as the 0.03 mm blur usually allowed for a sharp-looking print, so the softening can begin to show even in a normal-size print. Smaller sensors are enlarged more, so the same thing happens about one stop sooner on APS-C and two stops sooner on Micro Four Thirds.
None of that makes f/16 or f/22 wrong. If the near rocks and the far ridge both need to be sharp, a little even softness from diffraction looks better than one of them out of focus. It does mean the smallest aperture is a choice with a cost, not a default.
Try it in the simulator: get the nearest rocks and the far horizon both sharp without going past f/16, using where you focus as much as how far you stop down.
The photographers who named themselves after an aperture
In the early 1930s Ansel Adams, Edward Weston, Imogen Cunningham and a few others called their group f/64, after one of the smallest apertures on their large format view cameras. Stopping down that far was a statement: every grain of rock and every leaf sharp, set against the soft-focus pictorial style of the time. On a sheet of 8×10 inch film, f/64 gives about the same depth of field and diffraction as f/8.5 does on a full frame camera, because the film is about 7.5 times larger across. The f-number that counts as “a lot” depends on the format.
How to stop down on your camera
- Pick a mode that lets you set the aperture. Aperture priority (A or Av) or manual (M). In aperture priority you set the f-number and the camera chooses the shutter speed.
- Turn the aperture dial toward the higher numbers. On most cameras one dial changes aperture in these modes; on some lenses it is a ring on the lens barrel. Each click is usually a third of a stop.
- Watch the shutter speed. In aperture priority it doubles with each full stop. If it drops below what you can hold steady, raise the ISO or use a tripod. In manual, re-balance the exposure meter yourself.
- Check the result, not the viewfinder. Zoom in on the photo you just took, or use depth of field preview (next section), to see whether you have the depth you wanted.
Most phone cameras have a fixed aperture, so there is nothing to stop down. Their deep focus comes from the small sensor and short lens, and their blurred-background modes are made in software.
Stopped down and the shutter speed has fallen too far to hold? Camera shake explains the handheld limits and how to stay sharp below them.
Why the viewfinder does not show it: depth of field preview
Turn the aperture dial on most interchangeable lens cameras and nothing in the viewfinder changes. That is deliberate. The lens stays at or near its widest opening while you compose, because a wide opening gives a brighter view and lets autofocus work better, and it closes to your chosen setting only for the instant of the exposure. The catch is that what you see while composing has the shallow depth of the widest aperture, not the depth your photo will have.
The depth of field preview button closes the lens to the working aperture while you hold it. The view gets darker (on an optical viewfinder, much darker at f/16) and the background sharpens. Give your eye a few seconds to adjust and look at the edges of the zone you need sharp. Mirrorless cameras vary: some show the stopped down view all the time, many only while a preview button is held or with a menu setting turned on. The viewfinder and screen basics page covers the exposure preview settings.
One more quirk: on some fast lenses the plane of sharpest focus moves slightly as you stop down, called focus shift. The camera focuses wide open, so at a stop or two down the sharpest point can land just off your subject. If close-up shots at f/2.8 to f/4 look a little soft in exactly the wrong place, focus with the lens stopped down, or by magnified live view at the working aperture.
Stop-down metering
Stop-down metering means the camera measures the light with the lens already closed to the aperture you will shoot at, instead of wide open. Modern lenses tell the camera their aperture electronically, so it meters wide open and works out the result. Older manual lenses, lenses on adapters and some specialist lenses cannot, so the camera simply reads the light that comes through the lens as it is set.
In practice: set the aperture on the lens ring, and the view darkens as you stop down (a mirrorless camera often brightens it back for you). Aperture priority and manual both still work, because the meter sees the real light at the real aperture. Focus first with the lens wide open, where the view is brightest and the depth thinnest, then stop down to shoot. Some older film cameras worked the same way: you pressed a stop-down lever to take a reading. Using vintage lenses on a mirrorless camera covers the settings that make adapted lenses work.
Common mistakes when stopping down
- Thinking a bigger f-number means a bigger opening. The f-number is a fraction: f/16 is a sixteenth of the focal length across, much smaller than f/4.
- Going straight to f/22 “for maximum sharpness”. f/22 gives maximum depth, not maximum sharpness. Fine detail usually peaks two or three stops below wide open.
- Forgetting the shutter speed. Five stops down from f/2.8 is f/16, which needs a shutter 32 times longer. A sharp-focus landscape ruined by a shaky 1/15 second is a common result.
- Stopping down to fix a focus mistake. If you focused on the wrong thing, more depth only partly hides it. Focus where the depth will cover what matters, then stop down as much as you need.
- Stopping down when the light is too bright for the look you want. If you wanted a blurred background, stopping down to tame bright sun throws it away. Lower the ISO, raise the shutter speed, or use an ND filter instead.
- Judging depth from the viewfinder. It shows the widest aperture. Use preview or check the photo.
Want to know where to put the focus so a stopped down lens reaches all the way to the horizon? Hyperfocal distance shows how to find it and use it.
Try this: one scene, every stop
Ten minutes, any camera that lets you set the aperture, and a tripod or a steady wall.
- Find a scene with something close (a fence post or a flower about 1 m away) and something far (trees or buildings 30 m or more away).
- Set aperture priority and the lowest ISO. Focus on the near object and leave focus there.
- Take one frame wide open, then one at every full stop down to the smallest aperture: f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, or whatever your lens allows. Write down the shutter speed for each.
- Press depth of field preview, if your camera has one, at f/4 and at f/16, and compare what you see.
How to judge it: the shutter speed should double for each stop, which shows the light halving. Look at the far background frame by frame and note where it becomes acceptably sharp. Then zoom to 100 percent on the near object, in the center and in a corner: find the aperture where it is crispest, and the one where it starts to soften again. Those two apertures are your lens’s sweet spot and its diffraction limit, measured by you.
Want to check you can predict what stopping down will do before you press the shutter? The aperture and depth of field quiz tests it with explained answers.
Questions about stopping down
What does “stopped down” mean in photography?
It means the lens is set to a smaller aperture than its widest one, so the f-number is higher. “Stopped down two stops” means two full stops smaller than the lens’s maximum, for example f/5.6 on an f/2.8 lens.
Does stopping down make photos sharper?
Up to a point. The first two or three stops below wide open cut away the lens’s flaws and usually give the sharpest detail; beyond that, diffraction softens fine detail even as depth of field keeps growing. Sharper focus from front to back and sharper detail at the focus point are different things.
Does stopping down make the photo darker?
It lets in half the light per stop. In an automatic or priority mode the camera lengthens the shutter or raises the ISO so the photo looks the same brightness; in manual it gets darker unless you change one of those yourself.
Why doesn’t my viewfinder change when I stop down?
The lens stays wide open while you compose and closes only during the exposure, so the view stays bright and autofocus works well. Hold the depth of field preview button, if your camera has one, to see the real depth.
What is stop-down metering?
Measuring the exposure with the lens already closed to the shooting aperture. It is how cameras meter with manual, adapted and older lenses that cannot report their aperture setting, and it gives correct exposures in aperture priority or manual.
Is stopping down the same as closing down the aperture?
Yes. “Stopping down”, “closing down” and “using a smaller aperture” all mean moving to a higher f-number. The opposite is “opening up”.