Timing is the lynchpin in the whole mechanics of action photography. Often you only have a split second to take a picture, and if you hesitate the opportunity will be missed. As a result it's essential you're completely familiar with your equipment so you can use it instinctively.
A knowledge of the event you're photographing is also important, because it will enable you to predict the movements of your subject and prepare yourself to capture the action at its peak.
Depending upon the type of event you're photographing, two completely different techniques can be used - pre-focusing and follow-focusing.
Pre-focusing involves focusing on a point you know your subject will pass, such as a bend in a racetrack, a hurdle, a canoeist's slalom gate, or the bar in a high jump. All you do then is wait until your subject approaches and trip the shutter just before it reaches the point of focus. It's important to shoot just before your subject snaps into focus because the shutter takes a fraction of a second to open. The points generally chosen for pre-focusing tend to be places where the pace of action is slowed down, so you stand a better chance of capturing a perfect shot. Motorcyclists often travel at 150mph on a straight section of track, for instance, but at a corner that speed will be halved.
Follow-focusing involves tracking your subject with the camera and continually adjusting focus to keep it sharp. That way, when something exciting happens you're ready to capture it. This may sound straightforward enough, but follow focussing is very difficult and takes lots of practice to perfect.
Some of the latest auto focus systems can help, but don't rely on them completely. In servo mode the focus will adjust automatically to keep your subject sharp as it moves, and in predictive AF mode the camera will calculate the acceleration of you subject, and adjust focus at the moment of exposure to ensure a sharp result. The only problem with auto focusing is if something crosses your path the lens will hunt around and you'll miss the shot. Also some subjects move so fast that even the fastest AF systems can't keep up.
The actual shutter speed required to freeze movement depends upon three important factors; how fast your subject is travelling in relation to the camera.
If your subject is coming head-on, for example, you can freeze it with a slower shutter speed than if it's moving across the path. Similarly, a faster shutter speed will be required to freeze a subject that fills the frame than if it occupies a small part of it. The table below gives the minimum recommended speeds for common subjects.
|Subject||Across Path Half Frame||Across path Full Frame||Head-on|
|Car at 40mph||1/500s||1/250s||1/125s|
|Car at 70mph||1/1000s||1/500s||1/250s|
|Formula 1 car||1/2000s||1/1000s||1/500s|
Of course, you needn't always use a fast shutter speed. By intentionally introducing some blur you can add some drama to your picture. If you use a slow shutter and keep the camera still your subject will simply blur as it passes, while the background remains sharp.
A technique which works even more successfully, and can be used for just about any action subject, is panning. Again, a slow shutter speed is used, but instead of keeping the camera steady you track your subject with it by swinging your body, and trip the shutter while your moving. This produces am image where the subject comes out relatively sharp but the background blurs. The amount of blur created depends upon the smoothness of the pan and the shutter speed used.
As a starting point, use a shutter speed of 1/250s or even 1/500s with motor racing, 1/60 or 1/125s with cyclists and 1/30s with joggers. Once you gain confidence and your panning improves you'll be able to keep your subject sharp in the frame when using shutter speeds down to 1/2s or even longer.