What Is Motion Blur In Photography And How Should You Use It?

When photographing a moving subject with a fast shutter speed, all that motion will likely be frozen in the final image. As a result, your image may appear flat and lifeless. All the excitement and energy created by that movement is lost, and the resulting image looks static and rather disappointing.

There is a relatively simple solution to this issue – allow some of the 'right' kind of movement into the image, allowing either the moving subject or (if possible) its background to blur. Occasionally, you could perhaps even enable both to blur.

This blog gives you the full lowdown on motion blur in photography and explains how you can achieve it.

 

Table of contents

1. The art of the blur

2. Blurring the moving subject

3. Blurring the background

4. How much blur?

5. Use of neutral density (ND) filters

6. Putting it all together

 

The art of the blur

The technique is particularly associated with landscape photography, especially in blurring the movement of water. For instance, the sea, with waves rolling into shore, or a fast-flowing river running over and around rocks.

However, blurred motion photography is used not just for landscapes but also for sport, wildlife, people, and street life (particularly traffic after dark), whereby all kinds of activities can be blurred to give the sense of movement. So, the beating wings of a bird, the movements of a working person, and the colourful lines of traffic tail-lights are all great examples of commonly blurred moving subjects.

These ideas largely reflect the blurring of the moving subject, but there’s another blurring technique you can use. Specifically, that of blurring the background, not through it being out of focus, but through panning the camera to keep up with a fast-moving subject. This is frequently used in the photography of flying birds, fast-running mammals, a running athlete, or a fast car or train.

The aim of allowing blur into your moving-subject photos is to prevent them from becoming static. Instead, you’re instilling a sense of movement, energy and dynamism, a fundamental part of conveying mood and excitement in photographs that capture moving action, from a waterfall to a Formula One race.

 

Blurring the moving subject

In essence, this is very simple. For a subject moving at a slow or moderate speed, just put the camera on a tripod and use a long exposure, thus ensuring that anything moving in the frame will be blurred. If your subject’s moving really fast, then it may be possible to handhold the camera, with a shutter speed of 1/30 or 1/60 second slow enough to blur the movement.

Generally, however, tripod-mounting the camera with a shutter speed of 1/10 second or slower (up to many seconds) is needed. Here are some common scenarios in which you might need this:

  • Waves coming onto a shore
  • Water flowing in a stream
  • Urban traffic at dusk
  • Leaves blowing in a breeze

Of course, this blur can only be achieved within the limits of how far the lens aperture can be stopped down and how low the camera's ISO (the sensor's sensitivity) can be set. The narrower you have the aperture (i.e., the higher the f-number), the less light that is allowed through to the sensor, and hence the longer the shutter needs to be open in order to compensate. Similarly, the lower the ISO, the lower the sensor's sensitivity and the more light it needs to be correctly exposed.

Of course, there’s a limit to how narrow the lens aperture can be and how low the ISO can go. Once you've reached those limits, any attempt to make the exposure time longer will just allow too much light in and result in over-exposure.

So, blurring movement in bright sunlight of anything other than a fast-moving subject often requires adding a neutral density filter to the front of the lens and a filter that cuts down the amount of light getting into the lens. You also need to mimic low-light conditions – this is particularly useful for landscape photography. The use of neutral density (or ND filters) is covered below.

Generally, however, without the use of ND filters, blurred motion photography in which you're blurring the moving subject works best in relatively low light conditions. Unsurprisingly, this type is, therefore, best suited to dull, overcast conditions, in deep shade (such as in a woodland), at dusk, dawn, and at night.

 

Blurring the background

This technique is commonly used in sport and, to a lesser extent, wildlife photography, generally when photographing fast-moving action with a telephoto lens. It involves panning the camera as the subject moves past in front of you, from left to right or vice versa. You always keep the subject firmly in the frame and the camera's focus locked onto it. The background will become blurred, partially due to being out of focus, but mainly due to the lens's panning movement.

This can, in principle, be done with the camera on a tripod, but handholding gives you much greater flexibility and freedom to move quickly, which is an essential feature of this method. If you decide to handhold the camera, make sure you use a fast shutter to prevent the whole image from blurring through camera shake. Preventing the whole image from blurring is especially important when you come to use long focal length telephoto lenses.

Panning does take practice, and it isn't easy to get perfect results the first few times you try it. A good way to maximise the chances of success is to set the camera to continuous rapid shooting. Doing this will result in multiple images each time you pan on your subject (assuming you get more than one opportunity!).

There’s a danger that the camera will lose focus at some point while you’re panning, and it won't regain focus until your subject is far off in the distance. If you know the distance between you and your subject, and if that remains reasonably constant as your subject moves past, you can try to overcome potentially losing focus by turning the lens's autofocus off and manually pre-setting the focus to the necessary distance.

Some cameras now have automatic tracking, meaning that once a lens has focused on your chosen subject, the camera will keep it locked on, tracking the subject as it moves through the frame. This piece of technology generally works quite well, but it takes a bit of practice for you to understand how to make the best of it.

It can be frustrating to start with, but once you've mastered the art of panning and how to make the best use of your camera and telephoto lens combination, you can achieve spectacular results. Racing cars and horses, for example, can be pin sharp, with the background blurred out as a mass of horizontal lines, the result of elements in the background flying past the camera as the lens pans with your subject.

 

How much blur?

Just how much blur you need with either motion blur technique will depend on the effect you're trying to generate and how fast your subject is moving. For example, in terms of blurring the moving subject, when you’re photographing surf rolling onto a beach or a mountain stream babbling around rocks, an exposure of several seconds will cause the water to completely blur out.

A wave will become quite invisible, and be replaced by a very soft, often white, smooth silken effect containing very little detail. Though still depicting movement, such a total blur is actually very calming and will isolate a static object in the frame (such as a rock) from the rest of the view. It also removes – or at least masks – any clutter, greatly increasing the impact of the image and directing attention to that static object.

Replace that very long exposure with a rather faster one – say, one-tenth of a second – and the blur will become rather jagged, producing what I call a 'shards of glass' effect whereby sprays of water are clearly visible. The effect now is very restless and dynamic and very different from the smooth 'white-out' of the long exposure.

It's a similar thing with photography of evening traffic. How long the exposure needs to be very much depends on the amount of traffic and how fast it's going. However, an exposure of several seconds will usually be enough for the individual vehicles to become quite invisible and be replaced by colourful, continuous red tail-light lines.

It's a highly effective way of illustrating the evening life of any urban district. In this scenario, using a shorter exposure – such as one-tenth of a second – is less effective, as the vehicles become visible and the tail-light streams broken up into dashes that don't link up into a continuous stream.

When it comes to background blur generated by panning the camera on a fast-moving subject, the amount of blur is determined almost entirely by your subject's speed, something you have no control over. The camera has to pan at a speed that keeps up with your subject, and the amount of blur will reflect that panning speed.

Reducing your shutter speed won't have any influence, beyond perhaps, on the one hand, increasing the depth of field and hence the amount of the image technically in focus, and on the other increasing the risk of camera shake rendering the entire image blurred.

 

Use of neutral density (ND) filters

Commonly used in landscape photography, neutral density (ND) filters make it possible to use a slow shutter speed to blur a moving subject, even in bright sunlight. Not to be confused with neutral density graduated filters (ND grads), which are used to darken just one part of a scene that would otherwise be too bright, ND filters darken the whole scene, greatly increasing the exposure needed to create a photo.

Since they darken the entire frame evenly, they don't need to be rectangular (unlike ND grads) but can instead be standard circular filters that screw onto the front of your lens. Such filters come, of course, in various grades, offering mostly a 2-4 stop (i.e., 2 to 16-fold) reduction in the amount of light passing through. This is quite enough to allow for a slow enough shutter speed to give a good blur to surf or a stream, for example, even in bright sunlight.

It’s also possible to use filters called 'stoppers' that block out far more light, resulting in really long exposures that’ll blur out even a slow-moving sea or river into a featureless, often misty, and ethereal sheet. These filters are generally square and fit onto the front of a lens using the same kind of mount as is normal for ND grad filters. Their edges are also usually backed by a thin layer of foam to prevent any light leaking around their edges.

Stoppers are generally available in two strengths – six-stops, and 10-stops. These achieve 128-fold and 2048-fold reductions in the amount of light passing through, respectively. They may be very useful in creating an enormous amount of blur in moving water, for example, but sometimes it’s an overkill (particularly for the 10-stop stopper), with all detail lost in the blurred parts.

Moreover, they're quite difficult to use, as once they are mounted on the lens, it's quite impossible to see anything through the viewfinder or LCD screen, making it essential to line up the composition beforehand.

 

Putting it all together

The techniques of motion blur photography are mostly quite straightforward. However, the art can also be quite subtle, and the results never entirely predictable.

Things are on the move, of course, creating uncertainty, and slightly different exposure times can result in remarkably different end results.

The rule, then, is just to get out there and play. Experiment, take lots of different kinds of photos, with different compositions, different exposures, and hence different degrees of blur. You'll be amazed by the variety of results you'll achieve.

 

This blog was written by Nigel Hicks, a hugely experienced Devon-based professional photographer. Nigel works with the USA's prestigious National Geographic Image Collection, among many other bodies, and is a Fellow of the British Institute of Professional Photography.

Nigel runs regular photography workshops in southwest England. You can find out more about these here.

 

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