Using Motion Blur for Creative Effects
One of my goals during a visit to New Mexico's Bosque del Apache National Wildlife Refuge was to incorporate motion blur into some of my sandhill crane photographs. I wanted to use sharpness and softness in the image to help direct the viewer's attention, simplify the background, and convey a sense of the bird's motion. This dictated keeping the head, and especially the colorful eyes, relatively sharp. I use the word "relatively" because this type of image can often be successful with slightly less sharpness than would be required in a typical literal or documentary image. The sharpness difference between the eyes, head, and the rest of the image plays a significant role here, in addition to the absolute sharpness. The amount of softness that is acceptable in the face and eyes depends on the amount of blur in the rest of the image, and personal taste.
To accomplish the opposing goals of softness and sharpness in the same image, slower than usual shutter speeds are needed to create the blur. Keeping the crane's head relatively sharp is a matter of using a sturdy tripod with a leveled and balanced gimbaled head to allow very smooth and precise panning to follow the bird, and some luck. Because cranes and similar birds flex the muscles in their long necks to keep their heads still while their wings flap and the rest of their body is going through various contortions, such images are possible. The key is being able to smoothly and accurately follow the bird, keeping the bird's head as stationary as possible in the viewfinder as the shutter is released. As the birds land their head follows a very smooth line. This panning technique can often result in nice images. It can also result in many wasted exposures if the shutter speeds are very slow.
It should be noted that these images incorporate motion blur from two fairly independent sources. The first is the panning motion of the camera, which blurs all stationary objects in the image, like the image background. The second is the movement of the crane itself, which affects blurring of the wings, feet, and body, but often not the head. Very slow shutter speeds tend to show large amounts of blurring in both areas, often resulting in images that isolate the crane's head. As shutter speeds increase blurring in the crane diminishes much faster than does the blurring caused by panning the camera to follow the crane's motion. This often results in images that isolate the entire crane against a blurred background.
The same equipment and lens aperture setting was used to capture all of the images that follow. What matters here is the size of the subject in the frame, the subject's speed, and the camera's shutter speed setting, not the focal length or lens and camera model. For those who are curious, the captures were made with a Canon EOS 1Ds Mark II camera mounted to a Canon 600 mm F4 lens with Canon's 2X-II extender for a focal length of 1200 mm. The lens was stopped down one stop from maximum (F 5.6), and together with the two stops lost to the extender the shooting aperture was F 11. This setup was mounted and balanced on a Wimberly gimbaled tripod head which was in turn mounted on a large and discontinued Gitzo ball leveler in an old and very large 500 series Gitzo tripod. This tripod and leveler combination is very heavy but nearly unshakeable. A setup like this was required only due to the fact that the cranes were landing in an area I could not access more closely. Under different circumstances a focal length between 400 and 600 mm would work as well.
To illustrate the concepts more clearly, a more detailed view of each image below is displayed by moving your cursor over the image. A larger view of all the images is displayed by clicking on any image.

The Ballerina, Sandhill Crane
1/40 second, F11

In this image the crane's body is blurred due to its own motions while the foreground and background are blurred from panning the camera with the crane as it landed. Because the crane was traveling somewhat toward the camera, the foreground and background are not blurred as much by panning as they would be if the crane was traveling perpendicular to the axis of the lens. Even the bird's head is starting to show minor softening, but it is so much sharper than anything else in the image that it works well artistically. This is about as sharp as things get with moving subjects at these focal lengths and shutter speeds.  Photographing flying birds at this relative magnification using shutter speeds much slower than 1/40 second yields few useable results of this type. Time spent tying for this sort of image at shutter speeds in the neighborhood of 1/20 second might be better spent experimenting with even slower speeds for completely blurred abstract images.

Final Approach, Sandhill Crane
1/80 second, F11

Except for the crane's head, most of the image is quite blurred. The crane's body is blurred due to its own motions. Because the crane was moving at fairly high speed in a direction almost perpendicular to the lens axis, the foreground and background are very blurred from panning the camera to follow the bird. Maintaining sharpness in the crane's head at 1/80 second is significantly easier than it is using shutter speeds just one stop slower. Motion blurring in other areas such as the crane's wings is also significantly reduced. All things being equal, the distance over which the motion blurring will occur is cut in half. With the high ISO settings available today, getting a sharply "frozen" photograph is a much easier than properly controlling motion blur for creative effect. But keep in mind that the effect you want is more important than doing what is easy!

Touchdown, Sandhill Crane
1/160 second, F11

The crane's wings and feet were moving fast enough that there is quite a bit of motion blur in spite of the reasonably fast shutter speed. The small image size here does not make this quite as obvious as it actually is. The bird was almost landed and its horizontal speed was very low, resulting in minimal blur of the foreground and background from panning the camera to follow the bird. The presence of even a little motion blur helps quite a bit to obscure details in the foreground and background, which in turn helps to focus the viewer's attention on the crane. Everything in this image is at least slightly soft except the crane's head, which is quite sharp. At shutter speeds around 1/160 second and above, using good panning technique, sharpness in the bird's face is fairly easy to achieve. At the same time these shutter speeds greatly decrease the amount of motion blur everywhere else in the image. Some sense of motion remains in the wingtips, but it's nothing like that in our first example, which was shot at 1/40 second.

Sunset Landing, Sandhill Crane
1/250 second, F11
Here the motion blur in the bird's wings and feet is minimal but definitely present, while motion blur from panning the camera to follow the fast moving bird is much more pronounced. If not for the presence of significant motion blur, the background of this image would be much more distracting. Even at 1/250 second, nothing in this image is perfectly sharp except the crane's head and part of its neck. These are exceptionally sharp and help direct the viewer's eye. Unlike the first image in this series, the small amount of blur present in the crane's body dictates that the bird's face be perfectly sharp if the image is to succeed.
Even though many uncontrolled variables affect the results, there are a few general things we can learn from this exercise. It must first be noted that the specifics apply only to larger and therefore slower birds, photographed at a distance that keeps them fairly large in the frame, like the images above. Small birds move far more quickly. For example, a shutter speed of 1/3200 second was needed to capture a sharp image of a western bluebird swooping into its nest. And as far as blurring is concerned, it does not matter whether one is further away with a longer focal length or closer with a shorter focal length. All that matters is the size of the subject in the viewfinder. With this in mind one can see that:
1. Deliberately selecting slow shutter speeds when photographing flying birds is not necessarily a bad thing. It just depends on the kind of image you are trying to create.
2. The distance over which a moving subject is blurred doubles for every stop the shutter speed is lowered. Because of this, shutter speeds lower than those producing the desired effect will very quickly become unproductive because sharpness can not be maintained anywhere in the image.
3. At the slowest shutter shutter speeds (approximately between 1/40 and 1/80 second in these examples) dramatic motion blur effects in the bird itself as well as its background can be obtained.
4. At shutter speeds increase, images of the bird itself become much more literal, while the panning can still significantly blur the background if the bird is moving quickly.
5. Together with depth of field, motion blur can be an effective means of isolating the subject from its background.
More important than anything else that can be learned from this is to experiment with your photography. Doing only what has always worked will give the same results over and over. Experimentation can bring some surprises and add creativity to images, even if it does mean sacrificing a few opportunities for the cause.
Happy shooting,
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Copyright 2008 Dean M. Chriss
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