Motion Blur

Motion blur is the streak or smear left in a photograph by something that moved while the shutter was open. It is how a still picture records time, and it decides whether a frame looks frozen, fast, soft or simply wrong: unwanted, it is the most common reason a moving subject comes out unsharp; chosen on purpose, it is how photographers show speed, flow and energy.

Look at the stream above. The camera sat still for 1.3 seconds. Everything that did not move, the rocks, the moss, the split log, is sharp. The water, which travelled a long way in that time, became smooth white strands. That is the whole idea in one frame: the sensor adds up everything it sees while the shutter is open, so anything that changes position during the exposure is drawn along its path.

What makes a subject blur: four things, not one

Most explanations stop at “use a faster shutter speed“. Shutter speed matters, but it is only one of four things that decide how long the streak is. What counts is how far the subject’s image travels across the sensor during the exposure, and that depends on:

• Subject speed. A car at 100 km/h moves about 28 meters every second; a walker moves about 1.5.
• Exposure time. At 1/250 second the car moves 11 cm; at 1/30 second it moves almost a meter.
• Focal length. A longer lens magnifies the subject, and it magnifies the movement by the same amount.
• Distance. The same movement looks half as large from twice as far away. A jet crossing the sky at hundreds of km/h can look sharp at 1/250, while a dog trotting past your feet at the same shutter speed smears.

Put together, the streak on the sensor is roughly:

streak on sensor = subject speed × exposure time × focal length ÷ distance

Double the speed, the time or the focal length and the streak doubles. Double the distance and it halves. That one line explains almost every motion blur surprise.

A worked example: a runner at 10 meters

Take a runner moving at 5 m/s (a steady jog, 18 km/h) straight across the frame, 10 meters away, shot with a 50mm lens on a full frame sensor 36 mm wide with 6,000 pixels across. Each pixel is 0.006 mm wide. At 1/250 second the runner moves 2 cm. Scaled by 50 mm ÷ 10,000 mm, that is 0.1 mm on the sensor, or about 17 pixels.

Shutter speed	Runner moves	Streak on sensor	Streak, full file (6,000 px wide)	Streak seen on a phone (photo shown 1,200 px wide)
1/60	8.3 cm	0.42 mm	69 px	14 px, clearly smeared
1/125	4.0 cm	0.20 mm	33 px	7 px, visibly soft
1/250	2.0 cm	0.10 mm	17 px	3 px, nearly sharp
1/500	1.0 cm	0.05 mm	8 px	2 px, sharp
1/1000	0.5 cm	0.025 mm	4 px	1 px, sharp
1/2000	0.25 cm	0.0125 mm	2 px	under 1 px

The last two columns show something most guides skip: “sharp” depends on how big the photo will be seen. The same frame at 1/250 looks crisp on a phone and soft in a large print. Decide where the picture is going before you decide how fast is fast enough.

Direction changes everything

Only movement across the frame makes a streak. A subject coming straight at you mostly gets bigger, which barely blurs at all, so you can often use a shutter speed two stops slower than for the same subject crossing the frame. At 45 degrees, the sideways part of the movement is about 70 percent of the full speed (the cosine of 45 degrees is 0.71), so the streak is about 70 percent as long.

Parts of a subject move at different speeds

A runner’s torso might move at 5 m/s, but a hand or a foot on its forward swing moves much faster. A rolling wheel is the clearest case: the top of the tire moves forward at twice the vehicle’s speed, the hub at the vehicle’s speed, and the part touching the road is momentarily still. So a shutter speed that freezes a cyclist’s body can still leave the feet, the spokes and the top of the wheels blurred. When you check a frame, check the fastest part you care about, not the average.

Want to find the speed where a moving subject starts to streak? The camera simulator has a surfer to freeze, blur or pan with, a third of a stop at a time.

Or work it out for a subject of your own: pick what is moving, how far away it is and your lens, and see how far it smears at each shutter speed.

Starting shutter speeds for common subjects

These are starting points, whether you want to freeze motion or show it, for a subject crossing the frame at a moderate distance and filling a fair part of it. Move closer or zoom in and you need faster; step back or shoot head-on and you can go slower. Take one frame, check it at 100 percent, and adjust.

• Person walking: To freeze it: 1/250. To show movement: 1/15 to 1/30 (legs blur, body stays readable).
• Children playing, runner, dog running: To freeze it: 1/500 to 1/1000. To show movement: 1/30 to 1/60 with panning.
• Cyclist: To freeze it: 1/1000. To show movement: 1/15 to 1/30 panning.
• Bird in flight: To freeze it: 1/2000 or faster (small birds’ wings faster still). To show movement: 1/30 to 1/125 for wing blur on a sharp body.
• Car on an open road: To freeze it: 1/2000 or faster, or pan. To show movement: 1/30 to 1/60 panning.
• Splashing water drops: To freeze it: 1/2000 to 1/4000, or flash. To show movement: 1/4 to 2 seconds for silky water.
• Walking crowd: To freeze it: 1/250 to 1/500. To show movement: 1/4 second for streaks; 30 seconds or more to make people vanish.
• Car lights at night: To freeze it: Not practical. To show movement: 10 to 30 seconds on a tripod for continuous trails.

Two subjects should not be frozen. The tip of a 2 meter propeller turning at 2,400 rpm moves about 250 m/s (π × 2 m × 40 turns per second), so the blade sweeps 3.6 degrees of its circle at 1/4000 and almost 60 degrees at 1/250. Freeze it and the aircraft looks parked with its engine off. Photographers of propeller aircraft usually shoot around 1/60 to 1/250 to keep a visible disc, and helicopters, whose main rotors turn far more slowly, often need 1/60 or slower. Wheels are the same: a race car with crisp, frozen wheels looks stationary.

When you do want a subject frozen, how fast is fast enough for it? Shutter speed works it out in pixels of blur, from a person walking to a bird’s wings.

Need the camera to hold a shutter speed while it handles the rest of the exposure? Shutter priority mode lets you pick the speed and sets the aperture for you.

Subject blur, camera shake or missed focus: how to tell

A soft frame has several possible causes, and each needs a different fix. Image stabilization, for example, does nothing for a moving subject. Zoom in to 100 percent and look for these signs.

• The subject is streaked in one direction; still things around it are sharp: Cause: Subject motion. Fix: Faster shutter speed, flash, or pan with it.
• Everything is smeared, including things that cannot move; every point of light makes the same small squiggle: Cause: Camera shake. Fix: Faster shutter speed, image stabilization, a tripod, better handholding.
• Soft in every direction with no streak; something nearer or farther is sharp instead: Cause: Missed focus. Fix: Check focus point and mode, use continuous autofocus for moving subjects.
• Straight things lean or bend (poles, propellers, car bodies), but edges are crisp: Cause: Rolling shutter. Fix: Use the mechanical shutter, or step back or shoot more head-on so the subject crosses the frame more slowly.

Camera shake is not always the same across the frame. If the camera twists during the exposure, the corners can smear more than the middle. The steadier test is the one in the table: if anything that cannot move is sharp, the camera was steady and the blur came from the subject. Many frames have a bit of both, and then you need both fixes.

Not sure how slow you can go handheld before shake creeps in? The hand-holding rule gives a starting point for any lens.

Read the streak: working backward from a real photo

A streak is a measurement. If you know how long the exposure was, you can work out how fast the subject was going, and from that, the shutter speed that would have frozen it. The trick is to use the subject itself as a ruler, which means you do not need to know the distance or the focal length.

Take the taxi photo above, shot at 1/125 second. Zoomed in, the front and back edges of the car are smeared by roughly 2 percent of the car’s length. A sedan of this size is about 5 meters long, so it moved about 10 cm while the shutter was open:

• 10 cm in 1/125 second is 12.5 m/s, about 45 km/h. That is ordinary city traffic.
• Halve the time and you halve the streak: about 5 cm at 1/250, 2.5 cm at 1/500, a little over 1 cm at 1/1000.
• With the car filling about three quarters of the frame on a 6,000 pixel wide file, 1/1000 still leaves around a dozen pixels of smear at full size, which disappears on a phone screen. Truly frozen at full size would take about 1/4000.

Look at the wheels as well. They are more blurred than the body, because their surfaces turn as well as travel. That is the “parts move at different speeds” rule in a real frame. Was 1/125 wrong here? Not if the point of the picture is the still old building and a car passing through it. The blur says the moment was brief.

You can do this with any of your own frames: pick something of known size that moved with the subject, measure the streak against it, divide by the exposure time, and check your answer in the calculator above.

Using motion blur on purpose

Panning: a sharp subject on a streaked background

Panning means turning the camera to follow the subject during a slow exposure. The camera’s movement cancels the subject’s movement, so the subject lands on roughly the same part of the sensor and stays sharp, while the background, which is now the thing moving relative to the camera, streaks. Motion blur is about movement relative to the camera, not relative to the ground. That is also why panning needs a slow shutter speed, not a fast one: at 1/1000 the background freezes too and the picture looks like the vehicle is parked.

Start around 1/30 to 1/60 for cars, 1/15 to 1/30 for cyclists and runners, and faster, around 1/125 to 1/250, for fast vehicles on a long lens, where the background already streaks hard. Turn from the hips, start following before you press the shutter, and keep turning after it closes. Expect to keep a minority of frames; that is normal at slow speeds.

Practise the swing in the simulator: turn on Panning and find a shutter speed slow enough that the background streaks while the subject stays sharp.

Long exposures: smoothing water, ghosting crowds, drawing light

With the camera locked down on a tripod or a solid surface, a long exposure blurs only what moves. Moving water turns smooth from around 1/4 second, and silky by 1 to 2 seconds; see photographing waterfalls for how the look changes with time. Walking people become ghosts at fractions of a second and can disappear entirely in exposures of 30 seconds or more, because no one stays in one spot long enough to register. Car headlights and taillights become continuous light trails over 10 to 30 seconds, and moving a light yourself is light painting.

In daylight you usually cannot get a slow enough shutter speed even at the lowest ISO and a small aperture. An ND filter cuts the light: each stop doubles the exposure time, so a 6 stop filter turns 1/60 into about 1 second (1/60 × 64 = 1.07 s) and a 10 stop filter turns it into about 17 seconds (1/60 × 1,024). The exposure calculator does the arithmetic for any filter.

Try it in the simulator: in daylight, add an ND filter of 6 stops or more and get a correctly exposed frame at a shutter speed of 2 seconds or longer.

Only have a phone? Phone long exposure covers how phones blur water, lights and crowds, mostly by stacking many short frames.

Flash plus a slow shutter: frozen and moving in one frame

A flash burst is very short, typically a few thousandths of a second at full power and far shorter at low power, so wherever the flash is the main light, the flash duration, not the shutter speed, decides how sharp the subject is. Combine that with a slow shutter, a technique called dragging the shutter, and you get a sharp flash-lit subject plus a blurred trail from the ambient light. It is a staple of dance and event photography.

Timing matters. With normal front curtain sync, the flash fires at the start of the exposure and the ambient trail is recorded afterward, so it appears in front of the moving subject, which looks backward. Rear curtain sync fires the flash at the end, so the trail falls behind the subject the way the eye expects.

Moving the camera itself

Blur does not need a moving subject. Sweeping, twisting or shaking the camera during the exposure, called intentional camera movement, turns trees, flowers and city lights into painterly strokes. Zooming the lens during a half second or so exposure gives a zoom burst, with streaks radiating from the center. A useful variation is to hold still for the first part of the exposure, then move: you get a sharp base image with a motion layer on top.

Motion blur in video

Video has its own convention. Each frame is normally exposed for about half the frame interval, the “180 degree shutter” rule: 1/48 or 1/50 second at 24 fps, 1/50 at 25 fps, 1/60 at 30 fps, 1/100 at 50 fps. That amount of blur makes movement look smooth; much faster shutter speeds give the choppy, stuttering look of some action scenes. Camera settings for video covers the rest.

Check what you have read: one of these photos used a much longer exposure. Pick it, then read how you can tell.

Which photo used a longer exposure?

A B

Common mistakes and misconceptions about motion blur

• “Faster is always better.” Frozen wheels, props and rotors look parked, and a frozen waterfall can look like glass. Choose how much movement the picture should show, then set the speed.
• “Image stabilization or a tripod will fix a blurred subject.” They only stop the camera moving. A walking person at 1/15 on a tripod is still a smear.
• “There is one safe shutter speed.” 1/250 or 1/500 is safe for some subjects at some distances. Speed, distance, direction, focal length and final viewing size all change the answer.
• “Blur means the focus missed.” Focus blur is soft in all directions; motion blur streaks one way. Look for the direction before changing focus settings.
• “A long exposure blurs everything.” On a steady camera it blurs only what moved. If the rocks are soft too, the camera moved.
• “Panning needs a fast shutter.” The camera’s movement does the freezing. A fast shutter freezes the background as well and removes the sense of speed.
• Judging sharpness on the camera’s screen at full view. A 3 inch screen can hide 10 pixels of smear. Zoom to 100 percent on the subject’s fastest part before you move on.
• Using a slow speed when the moment needs to be crisp. Faces at a wedding ceremony or children’s expressions rarely benefit from blur. Decide what must be sharp first.

Want the whole range of choices for moving subjects in one place: freeze, blur or pan? Photographing moving subjects compares them side by side.

Try this: one subject at six shutter speeds

Find a place where people, cyclists or cars pass at a steady speed across your view, about 10 meters away: a sidewalk, a bike path or a quiet street. Set the camera to shutter priority with auto ISO, or use a phone app that lets you set the shutter speed. Spend 10 minutes:

1. With the camera held still, shoot passing subjects at 1/1000, 1/250, 1/60 and 1/15. Before each frame, predict the streak: each step is two stops, so it should be four times longer than the last.
2. Now pan with the subject at 1/30, then at 1/15. Take at least five frames at each.
3. Shoot one subject coming straight toward you at 1/250 and compare it with one crossing at 1/250.

How to judge the result: at 100 percent, find the speed where the body first looks sharp, then the speed where hands, feet or wheels also look sharp; they will differ. Measure one streak against the subject’s length, work out its speed as in the taxi example, and check it with the calculator. Then look at the frames at phone size and note how much slower you could have gone for that use. In the pans, count how many frames have a sharp subject; if none do, start following earlier and keep turning after the shutter closes.

Curious who first used blur as a deliberate style rather than a fault? Ernst Haas made blur a central part of his color work, decades after Eadweard Muybridge spent years trying to stop motion altogether.

Want to check you can choose between freezing, blurring and panning? Try the photographing moving subjects quiz.

Motion blur questions

What shutter speed stops motion blur?

It depends on how fast the subject’s image crosses the sensor, so there is no single number. As a start, 1/250 freezes a walking person, 1/500 to 1/1000 a runner or children playing, and 1/2000 or faster a bird in flight or a car close by. Check the fastest moving part at 100 percent and go faster if it still streaks.

Does image stabilization reduce motion blur?

Only the kind caused by the camera moving. Stabilization steadies the lens or sensor against your hands, but it cannot slow the subject down. For a moving subject, use a faster shutter speed, flash, or panning.

Why is my photo still blurred at 1/1000?

Either the subject is very fast, close or large in the frame, or the blur is not motion blur. Check whether it streaks in one direction (motion) or is soft all over (focus), and whether anything still is sharp. A long lens on a close subject can need 1/2000 or more.

How do I get motion blur in bright daylight?

Lower the ISO to its minimum and stop the aperture down to about f/11 to f/16, then add an ND filter if the shutter is still too fast. A 6 stop ND turns 1/60 into about 1 second; a 10 stop ND turns it into about 17 seconds.

Can I add motion blur afterward in editing?

Editors can add a directional blur to a selected area, and it can look convincing on simple subjects. Real motion blur follows the subject’s actual path, including the faster spin of wheels and limbs, which a filter has to fake. Getting it in camera is usually quicker and looks more natural.