Shutter speed is the main tool in the photographer’s arsenal for capturing great action shots. The ability to freeze a moment in time often makes the difference between a good shot and a great one. To take advantage of this concept, you should have a good grasp of the relationship between shutter speed and movement. When you press the shutter release button, your camera goes into action by opening the shutter curtain and then closing it after a predetermined length of time. The longer you leave your shutter open, the more your subject will move across the frame, so common sense dictates that the first thing to consider is just how fast your subject is moving.
Typically, you will be working in fractions of a second. How many fractions depends on several factors. Subject movement, while simple in concept, is actually based on three factors. The first is the direction of travel. Is the subject moving across your field of view (left to right) or traveling toward or away from you? The second consideration is the actual speed at which the subject is moving. There is a big difference between a moving sports car and a child on a bicycle. Finally, the distance from you to the subject has a direct bearing on how fast the action seems to be taking place. Let’s take a brief look at each of these factors to see how they might affect your shooting.
Direction of travel
Typically, the first thing people think about when taking an action shot is how fast the subject is moving, but the first consideration should actually be the direction of travel. Where you are positioned in relation to the subject’s direction of travel is critical in selecting the proper shutter speed. When you open your shutter, the lens gathers light from your subject and records it on the camera sensor. If the subject is moving across your viewfinder, you need a faster shutter speed to keep that lateral movement from being recorded as a streak across your image. Subjects that are moving perpendicular to your shooting location do not move across your viewfinder and appear to be more stationary. This allows you to use a slightly slower shutter speed (Figure 5.1). A subject that is moving in a diagonal direction—both across the frame and toward or away from you—requires a shutter speed in between the two.
Once the angle of motion has been determined, you can then assess the speed at which the subject is traveling. The faster your subject moves, the faster your shutter speed needs to be in order to “freeze” that subject (Figure 5.2). A person walking across your frame might only require a shutter speed of 1/60 of a second, while a cyclist traveling in the same direction would call for 1/500 of a second. That same cyclist traveling toward you at the same rate of speed, rather than across the frame, might only require a shutter speed of 1/125 of a second. You can start to see how the relationship of speed and direction comes into play in your decision-making process.
So now we know both the direction and the speed of your subject. The final factor to address is the distance between you and the action. Picture yourself looking at a highway full of cars from up in a tall building a quarter of a mile from the road. As you stare down at the traffic moving along at 55 miles per hour, the cars and trucks seem to be slowly moving along the roadway. Now picture yourself standing in the median of that same road as the traffic flies by at the same rate of speed; it appears to be moving much faster.
Although the traffic is moving at the same speed, the shorter distance between you and the traffic makes the cars look like they are moving much faster. This is because your field of view is much narrower; therefore, the subjects are not going to present themselves within the frame for the same length of time. The concept of distance applies to the length of your lens as well (Figure 5.3). If you are using a wide-angle lens, you can probably get away with a slower shutter speed than if you were using a telephoto, which puts you in the heart of the action. It all has to do with your field of view. That telephoto gets you “closer” to the action—and the closer you are, the faster your subject will be moving across your viewfinder.