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MODES By selecting different AF modes, you can further fine-tune the AF operation of your camera for specific shooting situations. You would rarely want the same AF style for a hockey game as you would for landscapes or product photography. ■ One Shot AF. Used primarily for still subjects. Pressing the shutter release halfway activates autofocus and achieves and locks focus. With evaluative metering, the exposure setting (aperture and shutter speed) is set when focus is achieved. The focus and exposure setting is locked as long as you continue to keep the shutter release pressed halfway. One Shot AF was used to get a tack-sharp image with the stationary subject shown in 3-12.
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CANON PHOTO WORKSHOP / Lens Basics
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■ AI Servo AF. Used when dealing with moving subjects where the focal distance keeps changing. When the shutter release is pressed halfway, the AF mechanism is activated and the camera focuses continuously. The exposure is set at the moment the shutter is released. I used AI Servo AF to make sure I got the shot in figure 3-13. ■ Predictive AF. If your camera has Predictive AF, you have even more fine control over your camera’s AF operation. If the subject approaches or retreats from the camera at a constant rate, the camera tracks the subject and predicts the focusing distance immediately before the picture is taken. With a manually selected AF point, the selected point tracks the subject and refocuses as needed.
MANUAL FOCUSING You may wonder why you should ever bother using the manual focus (MF) feature when your digital camera has such a sophisticated autofocus system. Isn’t AF much easier to use and doesn’t it always provide the right focal distance for your photos? The fact is, autofocus isn’t perfect. Because an autofocus system looks for patterns onto which it can lock on to focus (such as contrasting lines, patterns, etc.), difficult lighting situations, subjects that are very far away, macro photography, or conflicting focal points may result in your digital camera autofocusing incorrectly or being unable to focus at all. Often you have to compensate by using your manual focus ring. Also, you may want to intentionally blur a
ABOUT THIS PHOTO This unusual sign for a sardine factory
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sits right on the highway outside of Prospect Harbor, Maine. Taken with an EOS-1Ds Mark II, EF 70-200mm f/2.8L lens, ISO 100, 1/400 second at f/9. ©Jim White
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