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.
The compound microscope consists essentially of two or more double convex lenses fixed in the two extremities of a hollow cylinder. The lower lens (nearest to the object) is called the objective; the upper lens (nearest to the eye of the observer), the eyepiece. The cylinder is mounted upright on a screw device, which permits it to be raised or lowered until the object is in focus, i.e., until a clear image is formed. When an object is in focus, a real, inverted image is formed by the lower lens at a point inside the principal focus of the upper lens. This image serves as an "object" for the upper lens which produces another image larger still (but virtual) and visible to the eye of the observer.Computation of Magnifying Power
The magnifying power of a lens is commonly expressed in diameters. For example, if a lens magnifies an object 5 times, the magnification is said to be 5 diameters, commonly written simply "5x." The total magnification of a compound microscope is computed by multiplying the magnifying power of the objective by the magnifying power of the eyepiece.Development and Uses
The invention of the microscope is variously accredited to Zacharias Janssen, a Dutch spectaclemaker, c.1590, and to Galileo, who announced his invention in 1610. Others are known for their discoveries made by the use of the instrument and for their new designs and improvements, among them G. B. Amici, Nehemiah Grew, Robert Hooke, Antony van Leeuwenhoek, Marcello Malpighi, and Jan Swammerdam. The compound microscope is widely used in bacteriology, biology, and medicine in the examination of such extremely minute objects as bacteria, other unicellular organisms, and plant and animal cells and tissue—fine optical microscopes are capable of resolving objects as small as 5000 Angstroms. It has been extremely important in the development of the biological sciences and of medicine.Modified Compound Microscopes
The ultramicroscope is an apparatus consisting essentially of a compound microscope with an arrangement by which the material to be viewed is illuminated by a point of light placed at right angles to the plane of the objective and brought to a focus directly beneath it. This instrument is used especially in the study of Brownian movement in colloidal solutions (see colloid). The phase-contrast microscope, a modification of the compound microscope, makes transparent objects visible; it is used to study living cells. The television microscope uses ultraviolet light. Since this light is not visible, the apparatus is used with a special camera and may be connected with a television receiver on which the objects (e.g., living microorganisms) may be observed in color.
The electron microscope, which is not limited by the powers of optical lenses and light, permits greater magnification and greater depth of focus than the optical microscope and reveals more details of structure. Instead of light rays it employs a stream of electrons controlled by electric or magnetic fields. The image may be thrown on a fluorescent screen or may be photographed. It was first developed in Germany c.1932; James Hillier and Albert Prebus, of Canada, and V. K. Zworykin, of the United States also made notable contributions to its development. The scanning electron microscope, introduced in 1966, gains even greater resolution by reading the response of the subject material rather than the direct reflection of its beam. Using a similar approach, optical scanning microscopes achieve a resolution of 400 Angstroms, less than the wavelength of the light being used. Finally, the scanning tunnelling microscope, invented in 1982, uses not a beam but an electron wave field, which by interacting with a nearby specimen is capable of imaging individual atoms; its resolution is an astounding one Angstrom.
See C. Marmasse, Microscopes and Their Uses (1980).
Instrument that produces enlarged images of small objects, allowing them to be viewed at a scale convenient for examination and analysis. Formed by various means, the image is received by direct imaging, electronic processing, or a combination of these methods. The most familiar type of microscope is the optical, or light, microscope, in which lenses are used to form the image. Other types of microscopes use the wave nature of various physical processes, the most important being the electron microscope (see electron microscopy), which uses a beam of electrons in its image formation. Crude microscopes date to the mid-15th century, but not until 1674 were the powerful microscopes of A. van Leeuwenhoek able to detect phenomena as small as protozoa.
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A microscope (Greek: μικρόν (micron) = small + σκοπεῖν (skopein) = to look or see) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. The science of investigating small objects using such an instrument is called microscopy. The term microscopic means minute or very small, not visible with the eye unless aided by a microscope.
The first microscope was made around 1595 in Middleburg, Holland. Three different eyeglass makers have been given credit for the invention: Hans Lippershey (who also developed the first real telescope); Hans Janssen; and his son, Zacharias. The coining of the name "microscope" has been credited to Giovanni Faber, who gave that name to Galileo Galilei's compound microscope in 1625,. (Galileo had called it the "occhiolino" or "little eye".)
The most common type of microscope—and the first to be invented—is the optical microscope. This is an optical instrument containing one or more lenses that produce an enlarged image of an object placed in the focal plane of the lens(es). There are, however, many other microscope designs.
"Microscopes" can largely be separated into three classes: optical theory microscopes, electron microscopes, and scanning probe microscopes.
Optical theory microscopes are microscopes which function through the optical theory of lenses in order to magnify the image generated by the passage of a wave through the sample. The waves used are either electromagnetic (in optical microscopes) or electron beams (in electron microscopes). The types are the Compound Light, Stereo, and the electron microscope.
Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope.
Optical microscopes typically use refractive lenses of glass and occasionally of plastic or quartz, to focus light into the eye or another light detector. Mirror-based optical microscopes operate in the same manner. Typical magnification of a light microscope, assuming visible range light, is up to 1500x with a theoretical resolution limit of around 0.2 microns or 200 nanometers. Specialized techniques (e.g., scanning confocal microscopy) may exceed this magnification but the resolution is diffraction limited. Using shorter wavelengths of light, such as the ultraviolet, is one way to improve the spatial resolution of the microscope as are techniques such as Near Field Scanning Optical Microscopy.
Various wavelengths of light, including those beyond the visible range, are sometimes used for special purposes. Ultraviolet light is used to enable the resolution of smaller features as well as to image samples that are transparent to the eye. Near infrared light is used to image circuitry embedded in bonded silicon devices as silicon is transparent in this region. Many wavelengths of light, ranging from the ultraviolet to the visible are used to excite fluorescence emission from objects for viewing by eye or with sensitive cameras.
Two major variants of electron microscopes exist:
Microscopes measure up to production needs: today's microscopes have more capabilities and features to meet manufacturing demands. (Quality Test & Inspection).
Mar 01, 2003; Whether used in an assembly department, on a shop floor or in a metrology laboratory, the use of Microscopes is growing as...