A magnifying glass, an ordinary double convex lens having a
short focal length, is a simple microscope. The reading lens and
hand lens are instruments of this type. When an object is placed
nearer such a lens than its principal focus, i.e., within its
focal length, an image is produced that is erect and larger than
the original object. The image is also virtual; i.e., it cannot
be projected on a screen as can a real image. Sections in this
article: The Columbia Electronic Encyclopedia, 6th ed. Copyright
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