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A modern optical microscopeA modern optical microscope A microscope is an instrument that magnifies very small objects, allowing the viewer to see detail in the object that is invisible to the naked eye. Microscopes are used mostly—but not only—in biology and medical research. There are two main types of microscope: optical microscopes and electron microscopes. In an optical microscope, the image of the object is created by light. In an electron microscope, the image is created by a beam of tiny subatomic particles called electrons. Microscopes were first used for scientific research in the 17th century. The first electron microscopes appeared in the 1930s.

An optical micrograph of a fleaAn optical micrograph of a flea

Optical microscope

In an optical microscope, the image of the object is created by light. The simplest optical microscope is a magnifying glass, which contains a single lens. The lens gathers and bends light coming from the object, making the object look larger than it really is. Compound microscopes have more than one lens. A standard compound microscope has two groups of lenses. The first group, called the objective, gathers light from the object and focuses it to create a magnified image of the object. The second group, called the eyepiece, magnifies this image.

The world's most powerful optical microscope, announced in 2011, can see objects only 50 billionths of a metre (50 nanometres) across—small enough to see individual viruses. It works by using minute glass beads placed on the specimen to re-focus light into the microscope. It can magnify about 6500 times.

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