lens: Formation of Images
The image formed by a diverging lens is always virtual (cannot be projected on a screen as can a real image), erect (upright), and smaller than the object and is located on the same side of the lens as the object. The image formed by a converging lens depends on the position of the object relative to the focal length of the lens and the center of curvature. If the object is beyond the center of curvature, the image is real, inverted, and smaller than the object. As the object is brought toward the lens, the size of the image grows, becoming as large as the object when the object is at the center of curvature and larger than the object as the object is brought closer. When the object is one focal length away from the lens, however, no image at all is formed; and when the object moves closer than this distance, the image becomes virtual, erect, and larger than the object, as when one uses a magnifying glass.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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