Microscopes.

... The most widely used microscopes are optical microscopes, which use visible light to create a magnified image of an object. The simplest form of optical microscope is the double-convex lens with a short focal length. These lenses can magnify an object by up to 15 times. In general, however, a compound microscope is used, which has multiple lenses to provide more magnification than a single convex lens could alone. Some optical microscopes can magnify an object by 2,000 times or more. The compound microscope consists essentially of two lens systems, the objective and the ocular, mounted at opposite ends of a closed tube. The objective lens is composed of several lens elements that form an enlarged real image of the object being examined. The microscope lenses are set up so that the real image formed by the objective lies at the focal point of the ocular; the observer looking through the

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