Microscope instruments a story about them. Types of microscopes: description, main characteristics, purpose
Research on the topic: “What is a microscope? » PROJECT AUTHOR: 2nd CLASS STUDENT ELVINA KHAMIDULLINA LEADER: NIZAMOVA ELINA ZINAROVNA PRIMARY CLASS TEACHER
Goals and objectives of my research Goal: To explore the capabilities of the microscope for living and inanimate nature. Create your own microscope. Objectives: 1. Find out the history of the creation of the microscope. 2. Find out what microscopes are made of and what they can be. 3. Conduct experiments with research elements
Relevance of the project Isn't any of the schoolchildren interested in the structure of all life on Earth? We constantly ask the most difficult questions to dads, moms and teachers at school.
2. 1. History of the creation of the microscope. Microscope (from the Greek - small and looking) is an optical device for obtaining magnified images of objects invisible to the naked eye.
Biology teacher Svetlana Sergeevna very interestingly told the children what a microscope is and what can be seen by looking into it.
2. 4. Creating your own microscope. When we were looking for information about the history of microscopes, we learned on one of the sites that you can make your own microscope from a drop of water. And then I decided to try to conduct an experiment to create such a microscope
Creating a microscope To do this, you need to take thick paper, pierce a hole in it with a thick needle and carefully place a drop of water on it. The microscope is ready! Bring this droplet to the newspaper - the letters become larger. 
Conclusion By examining various objects under a microscope, a person learns the nature of life itself. While carrying out this project, we learned the history of the creation of the first microscope, and what people now use in modern life. We found answers to these questions in the school library encyclopedias, as well as on Internet sites.
The term "microscope" has Greek roots. It consists of two words, which when translated mean “small” and “I look.” The main role of the microscope is its use in examining very small objects. At the same time, this device allows you to determine the size and shape, structure and other characteristics of bodies invisible to the naked eye.
History of creation
There is no exact information in history about who was the inventor of the microscope. According to some sources, it was designed in 1590 by the father and son Janssens, eyeglass makers. Another contender for the title of inventor of the microscope is Galileo Galilei. In 1609, these scientists were presented with a device with a concave and convex lenses for public viewing at the Accademia dei Lincei.
Over the years, the system for viewing microscopic objects has evolved and improved. A huge step in its history was the invention of a simple achromatically adjustable two-lens device. This system was introduced by the Dutchman Christian Huygens in the late 1600s. The eyepieces of this inventor are still in production today. Their only drawback is the insufficient width of the field of view. In addition, compared to the design of modern instruments, Huygens eyepieces have an inconvenient location for the eyes.
A special contribution to the history of the microscope was made by the manufacturer of such devices, Anton Van Leeuwenhoek (1632-1723). It was he who attracted the attention of biologists to this device. Leeuwenhoek made small-sized products, equipped with one, but very strong lens. Such devices were inconvenient to use, but they did not double the image defects that were present in compound microscopes. The inventors were able to correct this shortcoming only 150 years later. Along with the development of optics, image quality in composite devices has improved.
Improvement of microscopes continues to this day. Thus, in 2006, German scientists working at the Institute of Biophysical Chemistry, Mariano Bossi and Stefan Hell, developed the latest optical microscope. Due to the ability to observe objects with dimensions as small as 10 nm and three-dimensional high-quality 3D images, the device was called a nanoscope.
Classification of microscopes
Currently, there is a wide variety of instruments designed to examine small objects. Their grouping is based on various parameters. This may be the purpose of a microscope or accepted method lighting, structure used for optical design, etc.
But, as a rule, the main types of microscopes are classified according to the resolution of microparticles that can be seen using this system. According to this division, microscopes are:
- optical (light);
- electronic;
- X-ray;
- scanning probes.
The most widely used microscopes are the light type. There is a wide selection of them in optical stores. With the help of such devices, the main tasks of studying a particular object are solved. All other types of microscopes are classified as specialized. They are usually used in a laboratory setting.
Each of the above types of devices has its own subtypes, which are used in one area or another. In addition, today it is possible to buy a school microscope (or educational), which is a system entry level. Professional devices are also offered to consumers.
Application
What is a microscope for? The human eye, being a special optical system biological type, has a certain level of resolution. In other words, there is a smallest distance between observed objects when they can still be distinguished. For normal eye this resolution is within 0.176 mm. But the sizes of most animals and plant cells, microorganisms, crystals, microstructure of alloys, metals, etc. are much less than this value. How to study and observe such objects? This is where different types of microscopes come to the aid of people. For example, optical devices make it possible to distinguish structures in which the distance between elements is at least 0.20 microns.
How does a microscope work?
A device with which to the human eye consideration of microscopic objects becomes available has two main elements. They are the lens and the eyepiece. These parts of the microscope are fixed in a movable tube located on a metal base. There is also an object table on it.
Modern types of microscopes are usually equipped with a lighting system. This, in particular, is a condenser with an iris diaphragm. A mandatory set of magnifying devices includes micro- and macroscrews, which are used to adjust the sharpness. The design of microscopes also includes a system that controls the position of the condenser.
Specialized, more complex microscopes often use other additional systems and devices.
Lenses
I would like to start describing the microscope with a story about one of its main parts, that is, the lens. They are a complex optical system that increases the size of the object in question in the image plane. The design of the lenses includes a whole system of not only single, but also two or three lenses glued together.
The complexity of such an optical-mechanical design depends on the range of tasks that must be solved by one or another device. For example, the most complex microscope has up to fourteen lenses.
The lens consists of the front part and the systems following it. What is the basis for constructing an image of the required quality, as well as determining the working condition? This is a front lens or their system. Subsequent parts of the lens are necessary to provide the required magnification, focal length and image quality. However, such functions are only possible in combination with a front lens. It is also worth mentioning that the design of the subsequent part affects the length of the tube and the height of the lens of the device.
Eyepieces
These parts of the microscope are an optical system designed to construct the necessary microscopic image on the surface of the retina of the observer's eye. The eyepieces contain two groups of lenses. The one closest to the researcher’s eye is called the ocular one, and the farthest one is the field one (with its help, the lens builds an image of the object being studied).
Lighting system
The microscope has a complex design of diaphragms, mirrors and lenses. With its help, uniform illumination of the object under study is ensured. In the very first microscopes this function carried out As optical instruments improved, they began to use first flat and then concave mirrors.
With the help of such simple details, rays from the sun or lamp were directed to the object of study. IN modern microscopes more perfect. It consists of a condenser and a collector.
Subject table
Microscopic preparations requiring examination are placed on a flat surface. This is the object table. Different kinds microscopes may have this surface, designed in such a way that the object of study will be rotated towards the observer horizontally, vertically or at a certain angle.
Operating principle
In the first optical device, a system of lenses gave an inverse image of micro-objects. This made it possible to discern the structure of the substance and the smallest details that were subject to study. The principle of operation of a light microscope today is similar to the work carried out by a refracting telescope. In this device, light is refracted as it passes through the glass part.
How do modern ones increase light microscopes? After a beam of light rays enters the device, they are converted into a parallel stream. Only then does the refraction of light occur in the eyepiece, due to which the image of microscopic objects is magnified. Next, this information arrives in the form necessary for the observer in his
Subtypes of light microscopes
Modern ones are classified:
1. By complexity class for research, work and school microscopes.
2. By area of application: surgical, biological and technical.
3. By types of microscopy: devices of reflected and transmitted light, phase contact, luminescent and polarization.
4. In the direction of the light flux into inverted and direct.
Electron microscopes
Over time, the device designed to examine microscopic objects became more and more sophisticated. Such types of microscopes appeared in which a completely different operating principle, independent of the refraction of light, was used. During use the latest types devices involved electrons. Such systems make it possible to see individual parts of matter so small that light rays simply flow around them.
What is an electron microscope used for? It is used to study the structure of cells at the molecular and subcellular levels. Similar devices are also used to study viruses.
The device of electron microscopes
What is the basis of the work the latest devices for viewing microscopic objects? How is an electron microscope different from a light microscope? Are there any similarities between them?
The operating principle of an electron microscope is based on the properties that electrical and magnetic fields. Their rotational symmetry can have a focusing effect on electron beams. Based on this, we can answer the question: “How does an electron microscope differ from a light microscope?” It, unlike an optical device, does not have lenses. Their role is played by appropriately calculated magnetic and electric fields. They are created by turns of coils through which current passes. In this case, such fields act similarly. When the current increases or decreases, the focal length of the device changes.
As for the circuit diagram, for an electron microscope it is similar to that of a light device. The only difference is that the optical elements are replaced by similar electrical ones.
Magnification of an object in electron microscopes occurs due to the process of refraction of a beam of light passing through the object under study. At various angles, the rays enter the plane of the objective lens, where the first magnification of the sample occurs. Next, the electrons travel their way to the intermediate lens. In it there is a smooth change in the increase in the size of the object. The final image of the material under study is produced by the projection lens. From it the image hits the fluorescent screen.
Types of electron microscopes
Modern types include:
1. TEM, or transmission electron microscope. In this installation, an image of a very thin object, up to 0.1 microns thick, is formed by the interaction of an electron beam with the substance under study and its subsequent magnification by magnetic lenses located in the lens.
2. SEM, or scanning electron microscope. Such a device makes it possible to obtain an image of the surface of an object with high resolution, on the order of several nanometers. Using additional methods such a microscope provides information that helps determine chemical composition near-surface layers.
3. Tunneling scanning electron microscope, or STM. Using this device, the relief of conductive surfaces with high spatial resolution is measured. In the process of working with STM, a sharp metal needle is brought to the object being studied. In this case, a distance of only a few angstroms is maintained. Next, a small potential is applied to the needle, resulting in a tunnel current. In this case, the observer receives a three-dimensional image of the object under study.
Microscopes "Leevenguk"
In 2002, it appeared in America new company, engaged in the production of optical instruments. Its product range includes microscopes, telescopes and binoculars. All these devices are distinguished by high image quality.
The company's head office and development department are located in the USA, in Fremond (California). But as for production capacity, then they are in China. Thanks to all this, the company supplies the market with advanced and high-quality products at an affordable price.
Do you need a microscope? Levenhuk will offer the required option. The company's range of optical equipment includes digital and biological devices for magnifying the object being studied. In addition, the buyer is offered designer models in a variety of colors.
The Levenhuk microscope has extensive functionality. For example, an entry-level teaching device can be connected to a computer and is also capable of video recording of the research being carried out. The Levenhuk D2L model is equipped with this functionality.
The company offers biological microscopes various levels. This and more simple models, and new items that are suitable for professionals.
Probably, each of us, at least once in our lives, had the opportunity to work with such a device as a microscope - some in school during a biology lesson, and others, perhaps, due to their profession. With the help of a microscope we can observe the smallest living organisms, particles. The microscope is a rather complex device, and besides, it has a long history, which will be useful to know. Let's figure out what a microscope is?
Definition
The word “microscope” comes from two Greek words “micros” - “small”, “skopeo” - “look”. That is, the purpose of this device is to examine small objects. If you give more precise definition, then a microscope is an optical device (with one or more lenses) used to obtain magnified images of certain objects that are not visible to the naked eye.
For example, microscopes used in today's schools are capable of magnifying 300-600 times, this is quite enough to see living cell in detail - you can see the walls of the cell itself, vacuoles, its nucleus, etc. But for all this, he went through quite a long path of discoveries, and even disappointments.
History of the discovery of the microscope
The exact time of the discovery of the microscope has not yet been established, since the very first devices for observing small objects were found by archaeologists in different eras. They looked like an ordinary magnifying glass, that is, it was a biconvex lens that magnified the image several times. Let me clarify that the very first lenses were made not of glass, but of some kind of transparent stone, so there is no need to talk about the quality of the images.
Later, microscopes consisting of two lenses were invented. The first lens is the objective, it addressed the object being studied, and the second lens is the eyepiece into which the observer looked. But the image of the objects was still greatly distorted, due to strong spherical and chromatic deviations - the light was refracted unevenly, and because of this the picture was unclear and colored. But still, even then the magnification of the microscope was several hundred times, which is quite a lot.
The lens system in microscopes was significantly complicated only at the very beginning of the 19th century, thanks to the work of such physicists as Amici, Fraunhofer, and others. The lens design already used a complex system consisting of collecting and diverging lenses. Moreover, these lenses were from different types glass that compensated for each other's shortcomings.
The microscope of a scientist from Holland, Leeuwenhoek, already had a stage where all the objects being studied were placed, and there was also a screw that allowed this table to be moved smoothly. Then a mirror was added - for better lighting objects.
Microscope structure
There are simple and complex microscopes. A simple microscope consists of a single lens system, just like a regular magnifying glass. A complex microscope combines two simple lenses.
A complex microscope, accordingly, provides greater magnification and, moreover, it has greater resolution. It is the presence of this ability (resolution) that makes it possible to distinguish the details of samples. An enlarged image, where details cannot be distinguished, will give us some useful information.
Complex microscopes have two-stage circuits. One lens system (objective) is brought close to the object - it, in turn, creates a resolved and enlarged image of the object. Then, the image is already magnified by another lens system (eyepiece), which is placed directly closer to the observer’s eye. These 2 lens systems are located at opposite ends of the microscope tube.
Modern microscopes
Modern microscopes can provide enormous magnification - up to 1500-2000 times, while the image quality will be excellent. Binocular microscopes are also quite popular; in them, the image from one lens is bifurcated, and you can look at it with two eyes at once (in two eyepieces). This allows you to distinguish visually small details much better. Such microscopes are usually used in various laboratories (including medical ones) for research.
Electron microscopes
Electron microscopes help us “examine” images of individual atoms. True, the word “consider” is used here relatively, since we do not look directly with our eyes - the image of an object appears as a result of the most complex processing of the received data by a computer. The design of a microscope (electronic) is based on physical principles, as well as the method of “feeling” the surfaces of objects with a very thin needle, the tip of which is only 1 atom thick.
USB microscopes
Nowadays, with the development of digital technology, everyone can purchase a lens attachment for their camera. mobile phone, and take photographs of any microscopic objects. There are also very powerful USB microscopes that, when connected to a home computer, allow you to view the resulting image on the monitor. Most digital cameras are capable of taking pictures in macro mode, with the help of which you can take photos of the smallest objects. And if you place a small converging lens in front of your camera lens, you can easily magnify a photo up to 500x.
Today, new technologies help us see what was inaccessible literally a hundred years ago. The parts of the microscope have been constantly improved throughout its history, and currently we see the microscope in its finished form. Although, scientific progress does not stand still, and in the near future, even more advanced models of microscopes may appear.
MICROSCOPE
an optical instrument with one or more lenses for producing magnified images of objects not visible to the naked eye. Microscopes can be simple or complex. A simple microscope is a single lens system. A simple microscope can be considered an ordinary magnifying glass - a plano-convex lens. A compound microscope (often called simply a microscope) is a combination of two simple ones. A compound microscope provides greater magnification than a simple one and has greater resolution. Resolution is the ability to distinguish details of a sample. An enlarged image in which details are indistinguishable provides little useful information. A complex microscope has a two-stage design. One system of lenses, called an objective, is brought close to the sample; it creates a magnified and resolved image of the object. The image is further magnified by another lens system called an eyepiece, which is placed closer to the viewer's eye. These two lens systems are located at opposite ends of the tube.
Working with a microscope. The illustration shows a typical biological microscope. The tripod stand is made in the form of a heavy casting, usually horseshoe-shaped. A tube holder is attached to it on a hinge, carrying all the other parts of the microscope. The tube in which the lens systems are mounted allows them to be moved relative to the sample for focusing. The lens is located at the lower end of the tube. Typically, a microscope is equipped with several objectives of different magnifications on a turret, which allows them to be installed in a working position on the optical axis. The operator, examining a sample, usually starts with the lens that has the lowest magnification and the widest field of view, finds the details that interest him, and then examines them using a lens with higher magnification. The eyepiece is mounted on the end of a retractable holder (which allows you to change the length of the tube when necessary). The entire tube with objective and eyepiece can be moved up and down to focus the microscope. The sample is usually taken as a very thin transparent layer or section; it is placed on a rectangular glass plate, called a slide, and covered on top with a thinner, smaller glass plate, called a coverslip. The sample is often stained chemicals to increase contrast. The glass slide is placed on the stage so that the sample is located above the central hole of the stage. The stage is usually equipped with a mechanism for smoothly and accurately moving the sample across the field of view. Under the object stage there is a holder for the third lens system - a condenser, which concentrates the light on the sample. There can be several condensers, and an iris diaphragm is located here to adjust the aperture. Even lower is a lighting mirror installed in a universal joint, which reflects the light of the lamp onto the sample, due to which all optical system microscope and creates visible image
. The eyepiece can be replaced with a photo attachment, and then the image will be formed on photographic film. Many research microscopes are equipped with a special illuminator, so that an illumination mirror is not necessary. Increase. The magnification of a microscope is equal to the product of the objective magnification and the magnification of the eyepiece. For a typical The magnification of the eyepiece is 10, and the magnification of the objectives is 10, 45 and 100. Therefore, the magnification of such a microscope is from 100 to 1000. The magnification of some microscopes reaches 2000. Increasing the magnification even more does not make sense, since the resolution does not improve; on the contrary, the image quality deteriorates.
Theory. A consistent theory of the microscope was given by the German physicist Ernst Abbe at the end of the 19th century. Abbe found that resolution (the minimum possible distance between two points that are separately visible) is given by
where R is the resolution in micrometers (10-6 m), l is the wavelength of light (created by the illuminator), μm, n is the refractive index of the medium between the sample and the lens, and a is half the input angle of the lens (the angle between the outer rays of the conical light beam , included in the lens). Abbe called the quantity numerical aperture (it is denoted by the symbol NA). From the above formula it is clear that the greater the NA and the shorter the wavelength, the smaller the resolved details of the object under study. The numerical aperture not only determines the resolution of the system, but also characterizes the lens aperture: the light intensity per unit image area is approximately equal to the square of NA. For a good lens, the NA value is approximately 0.95. The microscope is usually designed so that its total magnification is approx. 1000 NA.
Lenses. There are three main types of lenses, differing in the degree of correction of optical distortions - chromatic and spherical aberrations. Chromatic aberration occurs when light waves of different wavelengths are focused into different points on the optical axis. As a result, the image appears colored. Spherical aberrations are caused by the fact that light passing through the center of the lens and light passing through its peripheral part are focused at different points on the axis. As a result, the image appears unclear. Achromatic lenses are currently the most common. In them, chromatic aberrations are suppressed through the use of glass elements with different dispersions, ensuring the convergence of the extreme rays of the visible spectrum - blue and red - into one focus. A slight coloration of the image remains and sometimes appears as faint green stripes around the object. Spherical aberration can only be corrected for one color. Fluorite lenses use glass additives to improve color correction to the point that coloration is almost completely eliminated from the image. Apochromatic lenses are the lenses with the most complex color correction. They not only almost completely eliminate chromatic aberrations, but also correct spherical aberrations for not one, but two colors. Increasing apochromats for of blue color somewhat more than for red, and therefore they require special “compensating” eyepieces. Most lenses are "dry", i.e. they are designed to work in conditions where the gap between the lens and the sample is filled with air; the NA value for such lenses does not exceed 0.95. If a liquid (oil or, more rarely, water) is introduced between the objective and the sample, an “immersion” objective is obtained with an NA value as high as 1.4 and a corresponding improvement in resolution. Currently, the industry produces and various kinds special lenses. These include flat-field lenses for microphotography, stress-free (relaxed) lenses for working in polarized light, and lenses for examining opaque metallurgical samples illuminated from above.
Condensers. The condenser forms a cone of light directed at the sample. Typically, a microscope is equipped with an iris diaphragm to match the aperture of the light cone with the aperture of the objective, thereby providing maximum resolution and maximum image contrast. (Contrast in microscopy has the same important, as in television technology.) The simplest condenser, quite suitable for most general-purpose microscopes, is the two-lens Abbe condenser. Larger aperture lenses, especially oil immersion lenses, require more complex corrected condensers. Maximum aperture oil objectives require a special condenser that has oil immersion contact with the bottom surface of the slide on which the sample rests.
Specialized microscopes. Due to different requirements Science and technology have developed many special types of microscopes. A stereoscopic binocular microscope, designed to obtain a three-dimensional image of an object, consists of two separate microscopic systems. The device is designed for small magnification (up to 100). Typically applied to miniature electronic component assembly, technical inspection, surgical operations. A polarizing microscope is designed to study the interaction of samples with polarized light. Polarized light often makes it possible to reveal the structure of objects that lies beyond the limits of conventional optical resolution. A reflective microscope is equipped with mirrors instead of lenses that form an image. Since it is difficult to make a mirror lens, there are very few fully reflective microscopes, and mirrors are currently used mainly only in attachments, for example, for microsurgery of individual cells. Fluorescent microscope - illuminating the sample with ultraviolet or blue light. The sample, absorbing this radiation, emits visible luminescence light. Microscopes of this type are used in biology, as well as in medicine - for diagnostics (especially cancer). The dark-field microscope circumvents the difficulties associated with the fact that living materials are transparent. The sample is viewed under such “oblique” lighting that direct light cannot enter the lens. An image is formed by light diffracted by an object, causing the object to appear very light in color. dark background(with very high contrast). A phase contrast microscope is used to examine transparent objects, especially living cells. Thanks to special devices, part of the light passing through the microscope turns out to be phase-shifted by half the wavelength relative to the other part, which determines the contrast in the image. An interference microscope is further development phase contrast microscope. It involves interference between two light beams, one of which passes through the sample and the other is reflected. This method produces colored images that provide very valuable information when studying living material. see also
ELECTRON MICROSCOPE;
OPTICAL INSTRUMENTS;
OPTICS.
LITERATURE
Microscopes. L., 1969 Design of optical systems. M., 1983 Ivanova T.A., Kirillovsky V.K. Design and control of microscope optics. M., 1984 Kulagin S.V., Gomenyuk A.S. and others. Optical-mechanical devices. M., 1984
Collier's Encyclopedia. - Open Society. 2000 .
Synonyms:See what "MICROSCOPE" is in other dictionaries:
Microscope... Spelling dictionary-reference book
MICROSCOPE- (from the Greek mikros small and skopeo I look), optical instrument for studying small objects that are not directly visible to the naked eye. There are simple microscopes, or magnifying glasses, and complex microscopes, or microscopes in the proper sense. Magnifying glass... ... Great Medical Encyclopedia
microscope- a, m. microscope m.gr. mikros small + skopeo I look. An optical device with a system of highly magnifying glasses for viewing objects or parts of them that are not visible to the naked eye. BAS 1. Microscope, fine vision. 1790. Kurg. // Maltseva 54.… … Historical Dictionary of Gallicisms of the Russian Language
MICROSCOPE (Microscopus), a small constellation in the southern sky. Its brightest star has a magnitude of 4.7. MICROSCOPE, an optical instrument that allows you to obtain a magnified image small items. The first microscope was created in 1668... ... Scientific and technical encyclopedic dictionary
- (Greek, from mikros small, and skopeo I look). A physical apparatus for examining the smallest objects, which, through it, appear in an enlarged form. Dictionary of foreign words included in the Russian language. Chudinov A.N.,... ... Dictionary of foreign words of the Russian language
- (from micro... and...scope) an instrument that allows you to obtain an enlarged image of small objects and their details that are not visible to the naked eye. The magnification of the microscope, reaching 1500-2000, is limited by diffraction phenomena. Unarmed... ... Big encyclopedic Dictionary
Microtextiles, orthoscope Dictionary of Russian synonyms. microscope noun, number of synonyms: 11 biomicroscope (1) ... Synonym dictionary
MICROSCOPE, huh, husband. A magnifying device for viewing indiscernible objects with the naked eye. Optical m. Electronic m. (giving an enlarged image using electron beams). Under a microscope (in a microscope) examine what n. |… … Ozhegov's Explanatory Dictionary
- (from the Greek mikros small and skopeo I look), optical. a device for obtaining highly magnified images of objects (or details of their structure) invisible to the naked eye. Various types M. are intended for the detection and study of bacteria,... ... Physical encyclopedia
MICROSCOPE, microscope, man. (from the Greek mikros small and skopeo I look) (physical). An optical device with a system of highly magnifying glasses for viewing objects that cannot be seen with the naked eye. Ushakov's explanatory dictionary.... ... Ushakov's Explanatory Dictionary
An optical device for obtaining magnified images of objects that are not visible to the naked eye. In microbiol. light and electronic microscopy are used. One of the main indicators of microscopy is resolution - the ability to distinguish between two neighboring objects... ... Dictionary of microbiology
What is a microscope? Meaning and interpretation of the word mikroskop, definition of the term
microscope -
an optical instrument with one or more lenses for producing magnified images of objects not visible to the naked eye. Microscopes can be simple or complex. A simple microscope is a single lens system. A simple microscope can be considered an ordinary magnifying glass - a plano-convex lens. A compound microscope (often called simply a microscope) is a combination of two simple ones.
A compound microscope provides greater magnification than a simple one and has greater resolution. Resolution is the ability to distinguish details of a sample. An enlarged image with no details visible provides little useful information.
A complex microscope has a two-stage design. One system of lenses, called an objective, is brought close to the sample; it creates a magnified and resolved image of the object. The image is further magnified by another lens system called an eyepiece, which is placed closer to the viewer's eye. These two lens systems are located at opposite ends of the tube.
Working with a microscope. The illustration shows a typical biological microscope. The tripod stand is made in the form of a heavy casting, usually horseshoe-shaped. A tube holder is attached to it on a hinge, carrying all the other parts of the microscope. The tube in which the lens systems are mounted allows them to be moved relative to the sample for focusing. The lens is located at the lower end of the tube. Typically, a microscope is equipped with several objectives of different magnifications on a turret, which allows them to be installed in a working position on the optical axis. The operator, examining a sample, usually starts with the lens that has the lowest magnification and the widest field of view, finds the details that interest him, and then examines them using a lens with higher magnification. The eyepiece is mounted on the end of a retractable holder (which allows you to change the length of the tube when necessary). The entire tube with objective and eyepiece can be moved up and down to focus the microscope.
The sample is usually taken as a very thin transparent layer or section; it is placed on a rectangular glass plate, called a slide, and covered on top with a thinner, smaller glass plate, called a coverslip. The sample is often stained with chemicals to increase contrast. The glass slide is placed on the stage so that the sample is located above the central hole of the stage. The stage is usually equipped with a mechanism for smoothly and accurately moving the sample across the field of view.
Under the object stage there is a holder for the third lens system - a condenser, which concentrates the light on the sample. There can be several condensers, and an iris diaphragm is located here to adjust the aperture.
Even lower is a lighting mirror installed in a universal joint, which reflects the light of the lamp onto the sample, due to which the entire optical system of the microscope creates a visible image. The eyepiece can be replaced with a photo attachment, and then the image will be formed on photographic film. Many research microscopes are equipped with a special illuminator, so that an illumination mirror is not necessary.
Increase. The magnification of a microscope is equal to the product of the objective magnification and the magnification of the eyepiece. For a typical research microscope, the magnification of the eyepiece is 10, and the magnification of the objectives is 10, 45 and 100. Therefore, the magnification of such a microscope ranges from 100 to 1000. The magnification of some microscopes reaches 2000. Increasing the magnification even more does not make sense, since the resolution at the same time not improving; on the contrary, the image quality deteriorates.
Theory. A consistent theory of the microscope was given by the German physicist Ernst Abbe at the end of the 19th century. Abbe found that resolution (the minimum possible distance between two points that are separately visible) is given by
where R is the resolution in micrometers (10-6 m), . - wavelength of light (created by the illuminator), μm, n - refractive index of the medium between the sample and the lens, a. - half the input angle of the lens (the angle between the outer rays of the conical light beam entering the lens). Abbe called the quantity numerical aperture (it is denoted by the symbol NA). From the above formula it is clear that the greater the NA and the shorter the wavelength, the smaller the resolved details of the object under study.
The numerical aperture not only determines the resolution of the system, but also characterizes the lens aperture: the light intensity per unit image area is approximately equal to the square of NA. For a good lens, the NA value is approximately 0.95. The microscope is usually designed so that its total magnification is approx. 1000 NA.
Lenses. There are three main types of lenses, differing in the degree of correction of optical distortions - chromatic and spherical aberrations. Chromatic aberration occurs when light waves of different wavelengths are focused at different points on the optical axis. As a result, the image appears colored. Spherical aberrations are caused by the fact that light passing through the center of the lens and light passing through its peripheral part are focused at different points on the axis. As a result, the image appears unclear.
Achromatic lenses are currently the most common. In them, chromatic aberrations are suppressed through the use of glass elements with different dispersions, ensuring the convergence of the extreme rays of the visible spectrum - blue and red - into one focus. A slight coloration of the image remains and sometimes appears as faint green stripes around the object. Spherical aberration can only be corrected for one color.
Fluorite lenses use glass additives to improve color correction to the point that coloration is almost completely eliminated from the image.
Apochromatic lenses are the lenses with the most complex color correction. They not only almost completely eliminate chromatic aberrations, but also correct spherical aberrations for not one, but two colors. The magnification of apochromats for blue is slightly greater than for red, and therefore they require special “compensating” eyepieces.
Most lenses are "dry", i.e. they are designed to work in conditions where the gap between the lens and the sample is filled with air; the NA value for such lenses does not exceed 0.95. If a liquid (oil or, more rarely, water) is introduced between the objective and the sample, an “immersion” objective is obtained with an NA value as high as 1.4 and a corresponding improvement in resolution.
Currently, the industry produces various types of special lenses. These include flat-field lenses for microphotography, stress-free (relaxed) lenses for working in polarized light, and lenses for examining opaque metallurgical samples illuminated from above.
Condensers. The condenser forms a cone of light directed at the sample. Typically, a microscope is equipped with an iris diaphragm to match the aperture of the light cone with the aperture of the objective, thereby providing maximum resolution and maximum image contrast. (Contrast is as important in microscopy as it is in television technology.) The simplest condenser, quite suitable for most general-purpose microscopes, is the two-lens Abbe condenser. Larger aperture lenses, especially oil immersion lenses, require more complex corrected condensers. Maximum aperture oil objectives require a special condenser that has oil immersion contact with the bottom surface of the slide on which the sample rests.
Specialized microscopes. Due to the various requirements of science and technology, many special types of microscopes have been developed.
A stereoscopic binocular microscope, designed to obtain a three-dimensional image of an object, consists of two separate microscopic systems. The device is designed for small magnification (up to 100). Typically used for assembly of miniature electronic components, technical inspection, surgical operations.
A polarizing microscope is designed to study the interaction of samples with polarized light. Polarized light often makes it possible to reveal the structure of objects that lies beyond the limits of conventional optical resolution.
A reflective microscope is equipped with mirrors instead of lenses that form an image. Since it is difficult to make a mirror lens, there are very few fully reflective microscopes, and mirrors are currently used mainly only in attachments, for example, for microsurgery of individual cells.
Fluorescent microscope - illuminating the sample with ultraviolet or blue light. The sample, absorbing this radiation, emits visible luminescence light. Microscopes of this type are used in biology, as well as in medicine - for diagnostics (especially cancer).
The dark-field microscope circumvents the difficulties associated with the fact that living materials are transparent. The sample is viewed under such “oblique” lighting that direct light cannot enter the lens. The image is formed by light diffracted by an object, causing the object to appear very light against a dark background (with very high contrast).
A phase contrast microscope is used to examine transparent objects, especially living cells. Thanks to special devices, part of the light passing through the microscope turns out to be phase-shifted by half the wavelength relative to the other part, which determines the contrast in the image.
An interference microscope is a further development of the phase contrast microscope. It involves interference between two light beams, one of which passes through the sample and the other is reflected. This method produces colored images that provide very valuable information when studying living material. See also ELECTRON MICROSCOPE; OPTICAL INSTRUMENTS; OPTICS.
Microscope
an optical instrument with one or more lenses for producing magnified images of objects not visible to the naked eye. Microscopes can be simple or complex. A simple microscope is a single lens system. A simple microscope can be considered an ordinary magnifying glass - a plano-convex lens. A compound microscope (often called simply a microscope) is a combination of two simple ones. The stage is usually equipped with a mechanism for smoothly and accurately moving the sample across the field of view. As a result, the image appears colored. Spherical aberrations are caused by the fact that light passing through the center of the lens and light passing through its peripheral part are focused at different points on the axis. As a result, the image appears unclear. Larger aperture lenses, especially oil immersion lenses, require more complex corrected condensers. Maximum aperture oil objectives require a special condenser that has oil immersion contact with the bottom surface of the slide on which the sample rests. See also ELECTRON MICROSCOPE; OPTICAL INSTRUMENTS; OPTICS.
