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Working around autofocus

The intention of the autofocus feature of a digital camera is to free you from the responsibility of setting focus and improving the quality of your images. However honorable this intention may be, there are some situations when autofocus may not be your best ally, such as an off-center subject or a scene with low light. With a majority of digital cameras having only an autofocus optical system, learning how to beat the system will allow you to get these shots and open new creative techniques to explore.

How autofocus works

Let's examine how the autofocus system works. Digital cameras employ a number of focusing technologies to produce a clear picture. Some use an active autofocus system that emits an infrared light to measure the distance between the camera and the subject. The processor on the camera uses the distance measurement to adjust the focus motor behind the lens to bring that distance into focus. Others use a passive autofocus system, wherein the image sensor “looks” at the scene and sets focus based on various distances and color contrasts. Others measure subjects in certain areas of the frame and make adjustments according to preset focus values, such as multi AF (autofocus), center AF, or spot AF.


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