Microscope

Microscope

Only with the help of the development of microscopy technology was it possible to make even the smallest structures visible and thus overcome the natural limits of human vision. Without the development of microscopy technology, we would not have been able to achieve today's level of biological knowledge. For example, modern genetic engineering, molecular biology or medicine would be unthinkable without the extreme enlargement of cells, viruses, bacteria or other objects.

The beginnings of microscopy can already be seen in antiquity. Already around 500 BC The Greeks and Romans used magnifying glasses as firing glasses to enlarge objects, but it would be around 2,000 years before the first microscope was developed. Around 1637 ANTONY VAN LEEUWENHOEK (1632-1723) developed one of the first microscopes with which he was already able to study tooth decay, the growth of seeds, fruits, flowers and eyes of various animals.

The microscope is an optical device consisting of two lens systems, the objective and the eyepiece. A distinction is made between the light microscope and the electron microscope.

The principle of a light microscope is that of a thin, illuminated object using the lens, which acts like a converging lens, an enlarged image (image) is generated. This is then considered with the eyepiece (practically a magnifying glass), which enlarges the image even more. With a light microscope, however, a maximum of points with a distance of 0.001 mm can be distinguished (100 times what the human eye is capable of).

Therefore, with a 2,000-fold magnification of the object image, the possibilities of the light microscope are exhausted. Therefore, other options have been considered.

The result was the electron microscope. The French physicist LOUIS DE BROGLIE (1892-1987) sought ways to replace the light. In 1924, he realized that moving electrons have shorter wavelengths than light rays, can be bundled and used to scan extremely thin specimens. The electron microscope was "born". It was built in 1931 by the German ERNST RUSKA (1906-1988). This allowed an enlargement of the object image up to 2,000,000 times. In this way it was z. B. possible to recognize the structure of the finest structures of living things and viruses for the first time.

Structure of a microscope

Figure 2 shows the basic structure of a microscope. The microscope has two lens systems: the lens (objects) facing the lens and the eye facing eyepiece. Both systems act like converging lenses. Often several lenses of different focal lengths are available, which allow a different magnification.

The distance between the lens and the eyepiece is determined by the length of the tube. The tube is nothing more than an opaque tube.

The object is on the stage and illuminated from below. This can be done by a built-in lamp or by daylight, which is reflected by a mirror towards the object.

To get a sharp picture, the distance lens object can be changed using a drive wheel.

Mode of action of a microscope

The mode of action of a microscope can be seen from the ray path: With the objective, which faces the object, an enlarged, inverted, side-reversed and real (real) intermediate image of the object is generated. For this to be the case, the object must be between the single and the double focal length of the lens acting like a converging lens.

This intermediate image is viewed through the eyepiece. Since it is within the simple focal length of the eyepiece, the eyepiece looks like a magnifying glass. In other words, the intermediate image creates an enlarged, upright, right-sided and virtual (apparent) image of the object. This image can be viewed with the eyes and also photographed. It is an enlarged, reversed, page-swapped and virtual image of the object.

Magnification on the microscope

By magnifying the image of the object in two stages, a very large overall magnification of the image can be achieved with a microscope. Has z. For example, if the lens is magnified 40 times and the eyepiece is 8 times magnified, the overall magnification is 40 × 8 = 320

In a light microscope, magnifications of up to about 1,000 are used. If higher image magnifications are necessary, one usually uses electron microscopes.

Rules for handling a microscope

When working with a microscope, you should observe the following rules, which are also a convenient sequence of steps:

1. First place the slide with the object to be examined on the stage so that the object is above the opening! Clamp the slide!

2. To give you an overview of the object to be examined, set the smallest magnification with the nosepiece.

3. Move the lens to near the object by turning the drive wheel. Check from the side so that the lens does not touch the object, otherwise the lens and the object may be damaged.

4. Look through the eyepiece and focus on the subject by slowly increasing or decreasing the object lens distance by turning the drive wheel.

5. If necessary, adjust the brightness using the iris or mirror.

6. Now move the slide with the object on the stage until you have found a spot of the object that can be conveniently viewed.

7. Look closely at the object! Make an overview sketch.

8. Choose a higher magnification and look at the object again! Complete the sketch and label it.

Electron Microscopes

The resolution of a light microscope is limited by the wavelength of the light. In the thirties of the 20th century, electron microscopes were developed to achieve higher resolutions and therefore larger image magnifications. They work with electron beams and allow magnifications up to 500 000. Figure 5 shows the basic structure of such a microscope. The deflection of the electron beam is not done with lenses, but by means of magnetic or electric fields.

The development of such electron microscopes is now so advanced that they can also be used to image individual atomic structures. Figure 6 shows an example of this: the electron micrograph of a photonic crystal can be seen.

Manufacture of micro-preparations

Objects that are to be viewed with a microscope usually only have to be prepared for this purpose. It must be made a micro-preparation. For many dry objects (eg pollen, fish scales, hair, wings of insects) this is easy. They can be placed on a microscope slide without prior processing and examined microscopically. So they make dry preparations from them.

From other objects you make wet preparations. The objects are placed in a drop of water on the slide and covered with a coverslip.
In other objects, such as the elderberry, the cork or the pumpkin and corn stalk, only thin cuts must be made so that light can pass. Only then can these objects be viewed using the microscope.

The dry and moist preparations are fresh preparations. These usually do not last long. By special treatment micro-preparations can be made long lasting. The objects are enclosed in resin or gelatin. Such preparations are then called persistent preparations.

One differentiates between the micro-preparations fresh and long-term preparations. A micro-preparation consists of the slide, the object, often a containment medium (eg water) and a coverslip. If you want to examine all the details of the objects and look closely at them, the objects must be stained. So you need special colorants.

For the preparation of a micro-preparation, some equipment and chemicals are needed. In doing so, certain work steps must be adhered to.

History of Microscopy

Antiquity

As early as 500 BC, the Greeks and Romans used magnifying glasses as firing glasses to magnify objects. The findings of early research in the field of optics held by 1000 Alhazen (actually Ibn Al Haitam 965-1038) and described in the "Thesaurus Opticus" invented by him reading stone.

Middle Ages

Even in the Middle Ages, the development of new devices did not stagnate. In the 13th century, the English monk ROGER BACON (1214-1292) succeeded in grinding glass lenses for spectacles. The art of glass grinding was an important prerequisite for the invention of the microscope. It was fashion at the time to carry a "flea glass". It was a metal tube, the size of a thumb, with a lens at the end.

Around 1590, the Dutch eyewear maker ZACHARIAS JANSSEN (1588-1631) discovered that everything he viewed through two lenses in a row appeared magnified. He developed the composite microscope in this way, but did not pursue his discovery.

GALILEO GALILEI (1564-1642), Italian naturalist, improved the device developed by JANSSEN around 1609 and thus already examined the eyes of insects.

Almost at the same time, JOHANNES KEPLER (1571-1630), a German astronomer, was interested in optics and in 1611 developed the astronomical telescope, which consisted of two converging lenses.

A copy of the instrument developed by JANSSEN came into the possession of CORNELIUS DREBBEL (1572-1633), who studied and improved the instrument. This is how the composite microscopes developed by DREBBEL came into being, which arrived in 1622 in London and Rome.

17th century

In the 17th century, the composite microscope developed rapidly. One of the reasons for this was the many scientific researches and treatises in the field of physics, especially optics. For example, in 1637 the book "Dioptrique" by the philosopher and scientist RENÉ DESCARTES (1596-1650) on the law of refraction and in 1665 the work "Micrographia" by ROBERT HOOKE (1635-1703) was published, in which he published detailed microscopic drawings. In addition, he made his own lenses.

In 1666, ISAAC NEWTON (1643 1727) carried out its famous optical experiments. At that time he considered the achromatization impossible, since in his day the lenses of the microscope always divided the white light into its rainbow colors. Small objects were surrounded by color rings, which made it impossible to recognize minute details. Only about 100 years later, the researchers were able to construct achromatic microscopes.

The Dutch cloth merchant ANTONY VAN LEEUWENHOEK (1632-1723) built a "microscope" around 1637 according to his ideas and examined a variety of things - he observed the structure of seeds, fruits, flowers, eyes of various animals and the circulation of tadpoles, as well sperm. He made a separate microscope for each specimen and was one of the first to accurately record and describe the microscopic objects. He published his notes in scientific letters to the Royal Society of London. In 1683 he amazed the readers by stating that there were more creatures in his mouth than people in the Netherlands. The reason for this claim was the examination of the plaque of an eight-year-old boy. LEEUWENHOEK was the first to discover those living things that we now call bacteria. Since he was the secret of the art of lens-grinding, it was not until the nineteenth century that bacteria were able to be observed when the techniques of microscope construction were better mastered.

In 1669 MARCELLUS MALPIGHI (1628-1694) was the first to use the microscope for systematic biological investigations, and ROBERT HOOKE, an English scientist, discovered with his self-made microscope in 1667 that cork consists of small, separate "boxes" (cells). Thus, HOOKE was the discoverer of the plant cell.

Now the development of the microscope progressed rapidly: 1694 NICOLAAS HARTSOEKER (1654-1725) built the simple microscope with threaded tube, around 1700 CHRISTIAN HUYGENS (1629-1695) developed a two-eyepiece (Huygens eyepiece) with the field lens in front of the image plane of the objective ,

18/19. century

JAMES WILSON (1665-1730), GEORGE ADAMS (1708-1773) u. a. developed the microscopes further. WILSON's circular microscope was still working with reflected light, HERTEL (1683-1743) was already using transmitted-light illumination.

Around 1740, JOHANN NATHANIEL LIEBERKÜHN (1711-1756) reopened DESCARTES 'idea of ​​a concave mirror and constructed solar microscopes.

Around 1770 JAN (1715-1801) and HARMANUS (1738-1809) VAN DEYL built the first achromatic microscope objective.

MATTHIAS JAKOB SCHLEIDEN and THEODOR SCHWANN, German scientists, founded the cell theory: They assumed that cells are the basic building blocks of all plants and animals. A study of nature without microscopic examinations was unthinkable for her. Other scientists said that there was still enough to discover without a microscope. The small workshops continued to improve their microscopes.

ROBERT KOCH (1843-1910), a German bacteriologist, discovered the rod-shaped tubercle bacteria, the causative agents of tuberculosis, a vaccine that was at that time dangerous in 1882 with the help of the microscope.

It emerged companies for the production of mechanical-optical devices, eg. For example, from Carl Zeiss (1816-1888) in 1846 in Jena or the glassworks founded by OTTO SCHOTT (1851-1935) in 1884 for the melting and production of glass.

ERNST ABBE (1840-1905), German physicist, began there to develop the scientific basis for the construction of microscopes. In 1872 he developed the theory of image formation in the microscope. Subsequently, light microscopes were produced, the magnification of which is based on light penetrating from the specimen through two glass lenses, the objective lens and the eyepiece.

A constant improvement in the results of microscopy was also achieved by the invention of histological staining by JOSEPH VON GERLACH in 1855, with whose help, for example, body cells were more visible, and 1893 by the development of Köhler illumination with separate regulation of light field and condenser by AUGUST KÖHLER ( 1866-1948).

20-21. century

In the 20th century, the technology of the light microscope was further developed and overhauled. In 1903 HENRY SIEDENTOPF (1872-1940) and RICHARD ZSIGMONDY (1865-1929) developed the ultramicroscope. In 1925 they received the Nobel Prize for this development. In 1904 her invention was also overhauled and the ultraviolet microscope was made by AUGUST KÖHLER and MORITZ VON ROHR (1868-1940). In 1911 CARL REICHERT (1851-1922) developed the luminescence microscope.

In 1931 ERNST RUSKA (1906-1988) and MAX KNOLL (1897-1969) succeeded in developing the first electron microscope. It works on a similar principle as the light microscope. However, the light beam is replaced by an electron beam and the optical lenses are replaced by electromagnetic lenses. Because of this, the resolution of the electron microscope is much higher than that of the light microscope.

In 1941, FRITS ZERNIKE (1888-1966) invented the phase contrast, with the help of which it is possible to obtain high-contrast images in a light microscope without having to dye them in advance. For this discovery, he received the 1953 Nobel Prize.

In the 21st century, the electron microscopes were then improved and further developed.

Using the so-called scanning tunneling microscope developed in 1981, even atoms can be viewed. The development of the Scanning Tunneling Electron Microscope and similar microscopes has made it possible to view, process or produce in areas of one millionth of a millimeter. Its inventors, GERD BINNIG (* 1947) and HEINRICH ROHRER (* 1933), were awarded the Nobel Prize for Physics in 1986 for their work.

In 1985, WIJNAENDTS VAN RESANDT demonstrated "optical cutting", which makes it possible to obtain a three-dimensional image of the object to be microscoped.