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How Lenses Work

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How a High-Tech Motor Moves the Lens

Any automatic focusing camera must have a motor to move the lens elements to bring the subject into focus. That’s not a simple task when you consider how much speed and precision the camera requires and how little space the lens provides to hide a motor. As with the autofocus mechanisms devised to measure the distance from camera to subject, camera makers have come up with several ingenious ways to slip motors into minuscule spaces. We’ll look here at a motor designed by Canon that many other camera manufacturers have adapted: the ultrasonic motor (USM).

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