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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.

A typical compound optical microscopeA typical compound optical microscope

Parts of an optical microscope

The eyepiece of a microscope is a cylinder containing two or more lensesTypical magnifications for eyepieces are 2 times, 10 times and 50 times. The eyepiece brings the image into focus on the eye. The objective is another cylinder containing a compound lens. There will usually be three or four objective lenses fixed to an objective turret, or revolving nosepiece. This can be rotated manually to select one of the objectives, and thus obtain different magnifications. Some objective lenses on research microscopes have a magnification of 200 times.

The magnification of a compound optical microscope is the product of the magnification of its eyepiece and objective lens (e.g. 10 x 200 = 2000).

The platform below the objective where the specimen, fixed to a transparent slide, is placed is called the stage. A hole in the centre allows light to pass through it to illuminate the specimen from below. The eyepiece or objective barrel is moved up and down for focus by using adjustment knobs: one for coarse and one for fine focusing. Most microscopes have their own light source, usually a halogen lamp, LED or laser. The light is focused on to the specimen by a condenser.

Micrograph of a snow crystal Micrograph of a snow crystal


The image from an optical microscope can be photographed to produce a micrograph. In a digital camera, a charge-coupled device (CCD) allows the capture of digital images. A digital microscope is a microscope fitted with a digital camera which allows observation of a specimen using a computer: the image is shown directly on a computer screen without the need for an eyepiece.

The microscope used by Anton van LeeuwenhoekThe microscope used by Anton van Leeuwenhoek

Early inventions

The first compound microscope was probably built by Dutch spectacle-maker Zacharias Janssen in about 1590. Early microscopes had poor-quality lenses and gave blurred images. In the 1670s another Dutchman, Anton van Leeuwenhoek, began making simple, single-lens microscopes. He was the first person to see micro-organisms, such as bacteria and amoebae.

Hooke's microscopeHooke's microscope

Microscopes for research

Scientists first began to use microscopes for research in the 17th century. English scientist Robert Hooke (1635–1703) published a book called Micrographia in 1665 which contained a series of accurate drawings of specimens he had studied under a microscope, including insects, fungi and snowflakes. Using his microscope he was able to discover, for example, how nettles sting and the existence of cells—the building blocks from which all living things are made. By the 19th century, microscopes were much improved, with a far greater degree of magnification. Scientists already suspected that there was a connection between "germs" (micro-organisms such as bacteria) and disease. French scientist Louis Pasteur (1822–1895) was able to observe bacteria through a microscope and prove beyond doubt that bacterial infection caused diseases in both animals and humans.
Louis Pasteur studying bacteria under a microscopeLouis Pasteur studying bacteria under a microscope

 Chris Oxlade


  • c.1590
    Zacharias Janssen builds the first compound microscope.
  • 1665
    English scientist Robert Hooke publishes Micrographia, a collection of his observations using a microscope.
  • 1683
    Anton van Leeuwenhoek develops a high-precision microscope.
  • 1932
    The first electron microscope is built by Ernst Ruska and Max Knoll. It is a transmitting electron microscope (TEM).
  • 1935
    The first scanning electron microscope (SEM) is built by Ernst Ruska.
  • 1981
    German physicist Gerd Binnig and Swiss physicist Heinrich Rohrer develop the first scanning tunnelling electron microscope (STM).

See also in Technology

See also in Science

See also in Life

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.

Police use microscopes to solve crimes, for example, by finding particles of clothing or hairs from a suspect at the scene of a crime.

Using a microscope fixed above a patient in an operating theatre, surgeons are able to carry out microsurgery. Sewing together tiny nerves or blood vessels can be undertaken while looking at the body part through a microscope.

The world's smallest microscopes are threaded through endoscopes, instruments used to examine inside the human body. About the width of small coins, they have no lenses: just a light and a sensor to capture images of individual cells.

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