Magnifying glass
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A magnifying glass is a single convex lens which is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. The magnifying glass is the simplest form of optical microscope.
A magnifying glass works by creating a magnified virtual image of an object behind the lens. The distance between the lens and the object must be shorter than the focal length of the lens for this to occur.
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The framed lens may be mounted on a stand, keeping the lens at the right distance from the table, and therefore at the right distance from the object on the table. The latter applies if the object is small, and also if the height is adjustable. Some magnifying glasses are foldable (from the handle or stand).
A sheet magnifier consists of many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner. This arrangement is known as a Fresnel lens.
The magnifying glass is an icon of detective fiction, particularly that of Sherlock Holmes.