Friday, September 1, 2006
How to turn moving subjects into moving photos
Use continuous AF for action subjects. Not only does this mode continuously focus on the moving subject, but it automatically provides predictive AF (also known as focus tracking) when the camera detects a moving subject. The AF system makes successive focus readings and from those calculates the subject's speed and direction of movement. The camera's onboard processor then uses this data to predict the subject's position at the exact instant of exposure and adjusts focus accordingly, compensating for the distance the subject travels during the short lag between the moment you fully depress the shutter button to make the exposure and the moment the exposure is actually made.
Track the subject through the viewfinder before it reaches the point at which you wish to capture it, pan the camera to follow the subject's travel, press the shutter button halfway down to activate the AF system, give the system a moment to do its thing, then fully depress the shutter button to make the exposure as the decisive moment arrives. Keep panning the camera with the subject as you depress the shutter button; if you stop panning as you shoot, the subject likely will blur.
If your moving subject will pass a known point, such as a racing car going through a specific corner or a baseball player stealing second base, you can manually prefocus on that point, then shoot as the subject arrives. This assures sharp focus and eliminates the delay of autofocusing. Of course, you can't prefocus with random action, such as soccer, or with subjects that don't offer a spot to prefocus upon, such as birds in flight.
Not every shot will be perfect. In fact, with erratically moving subjects, such as swallows shagging bugs in mid-air, the success percentage can be quite low. So don't get discouraged if you have more tossers than keepers—all action photographers do. Your percentage will go up with practice, but there will always be unsharp, poorly exposed and badly framed shots. This is one reason why lots of action shooters have gone digital: the cost per shot is much less.
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