The device of a microscope, the structure of a microscope. Optical parts of a microscope What does the mechanical part of a light microscope consist of?
Word " microscope“comes from two Greek words “micros” - “small”, “skopeo” - “I look”. That is, the purpose of this device is to examine small objects. To give a more precise definition, a microscope is an optical device ( with one or more lenses), used to obtain enlarged 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 a 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 they were already invented microscopes, consisting of two lenses. 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 made of different types of glass, compensating for each other’s shortcomings.
Microscope A scientist from Holland, Leeuwenhoek already had a subject table 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 illumination of 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. Difficult microscope, accordingly, gives greater magnification, and besides, 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 ( lens) 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), it 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. Similar microscopes are usually used in different laboratories ( including in medical) 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 a method of “feeling” the surfaces of objects with a very thin needle, the tip of which is only 1 atom thick.
USB microscopes
Currently, with the development of digital technology, everyone can purchase a lens attachment for the camera of their 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 photography, with its help 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. Parts microscope Throughout its history, they have been constantly improved, and currently we see the microscope in its finished version. Although, scientific progress does not stand still, and in the near future, even more advanced models of microscopes may appear.
Video for children. Learning to use a microscope correctly:
MICROSCOPE. MICROSCOPIC DEVICES.
Microscopic technique.
The main stages of cytological and histological analysis:
Selecting a research object
Preparing it for examination under a microscope
Application of microscopy methods
Qualitative and quantitative analysis of acquired images
Quantitative research methods - morphometry, densitometry, cytophotometry, spectrofluorometry.
Microscopic research methods are of great importance for the theory and practice of medicine as a way to study histological structures in normal conditions, experiments and pathologies.
Light microscope. A microscope is an optical device designed to obtain magnified images of biological objects and details of their structure that are invisible to the naked eye.
A microscope consists of optical and mechanical parts. Optical parts of the microscope: objectives, eyepieces, mirror and condenser with iris diaphragm. Mechanical parts of the microscope: base, tube holder, tube, revolver, stage, macro- and microscrew mechanisms, condenser movement mechanism
Optical parts of the microscope.
Lens– the main optical part of the microscope, which creates an image of the drug. The lens is a system of lenses in a metal frame, where there is a frontal - the main or magnifying lens, closest to the object, which builds the image and correction - they eliminate the aberrations of the front lens. Lenses are divided into:
A) according to the degree of magnification for low magnification lenses (magnification ≤10), medium magnification lenses (magnification ≤40), high magnification lenses (magnification ≥40),
B) according to the degree of perfection of corrections of aberrations (distortions) into monochromats (designed to work under monochromatic lighting), achromats (chromatic aberration corrected for 2 colors of the spectrum), apochromats (chromatic aberration corrected for 3 colors of the spectrum); planmonochromats, planchromats, planapochromats (image surface curvature corrected),
C) according to dry-air and immersion properties. When using dry-air lenses, there is an air space between the preparation and the lens; with immersion lenses, there is a liquid (immersion oil, water) between the preparation and the lens. Accordingly, immersion lenses are divided into water and oil. Obtaining maximum magnification is possible only with the help of an immersion objective (usually an objective with a magnification of 90). Immersion objectives are designed to work with coverslips no thicker than 0.17 mm.
Eyepiece– an optical system used to view the image created by the lens. A simple eyepiece (Huygens) consists of two plano-convex lenses, with their convex surface facing the objective. Between the lenses is a diaphragm with a constant opening. An arrow - pointer - is attached to the diaphragm. The upper lens is called the eye lens; the magnification of the eyepiece is indicated on its frame. The lower lens is called the field lens. The eyepiece usually magnifies the image 5-25 times
Mirror– directs the light stream through the condenser onto the drug. It has flat and concave surfaces, which are used depending on the degree of illumination.
Condenser– collects light rays and focuses them on the drug, providing sufficient and uniform illumination of the latter. The condenser consists of two lenses: a lower biconvex lens and an upper plano-convex lens. Using a condenser, the degree of illumination of the object being studied is adjusted.
Topic 1. CELL
§6. STRUCTURE OF A MICROSCOPE
You familiarize yourself with structure microscope and learn how to calculate its magnification.
Will we work with a microscope?
What can you see with a microscope besides bacteria?
Microscope (from the Greek “micros” - small and “skopeo” - look, examine) - is a magnifying device that allows you to examine an object of a very small size. The design of the school microscope is almost the same as in the best research microscopes of the first half XX century. (Jr. 6). With the correct settings, a school microscope allows you to see not only the cell, but also its individual internal structures. And if you have some experience, you can even perform some interesting experiments.
A microscope consists of a body and elements of the optical system through which light passes.
The parts of the body are:
✓ base;
Rice. V. Appearance and main components of a school microscope
✓ the object stage on which the prototype is placed is fixed on the table using two flexible holders;
In a tripod with a variable tilt angle, on which there is a large screw for coarse clarity adjustment (macro screw) and a smaller screw for fine adjustment of clarity (micro screw);
✓ a tube on the lower part of which a revolving attachment with lenses is attached, and an eyepiece is placed in the upper part.
The elements of the optical system of the microscope include:
✓ concave mirror that can be rotated;
In the diaphragm, which is located under the stage;
✓ revolving attachment with lenses of different magnifications;
✓ eyepiece through which the object of study is observed.
A mirror is used to adjust the best illumination of the preparation. The aperture regulates the contrast and brightness of the image: if the aperture is closed, the image is very contrasty, but dark; if the aperture is fully open, then the contrast is low and there is a lot of light, so the image is over-brightened.
Rice. 7. Objectives (a), eyepiece (b) of a school microscope and their markings
Objects. The school microscope has three lenses: very low (4x), low (10x) and high (40x) magnification. To make them easy to change, they are screwed into the revolving attachment. The lens, which is located vertically downwards, towards the object of study, is included in the optical system, the others are turned off. By turning the turret, you can change the working lens and thus move from one magnification to another. When you connect another lens to the optical system, a slight click is heard - this is the spring lock of the revolving attachment.
The lens is the main element of the microscope's optical system. The numbers on the lens indicate its technical characteristics.
In the top line, the first number indicates the lens magnification (position 7).
The product of the objective magnification and the eyepiece magnification shows the overall magnification of the microscope. For example, with the 4x objective and 10x eyepiece turned on, the total magnification of the microscope is: 4 ∙ 10 = 40 (times).
When working with a microscope, a prototype is placed on the stage, secured with holders, and a low-magnification lens (10x) is turned on. By rotating the mirror, light is directed onto the preparation, and macroquint adjust clarity. Next, if necessary, turn on the high-magnification lens, adjust the clarity with a microscrew and contrast the image with the aperture.
When working with a microscope, adhere to the following rules:
1. Eyepiece and objective lenses must be protected from contamination and mechanical damage: do not touch them with fingers or hard objects, do not allow water or other substances to come into contact with them.
2. It is prohibited to unscrew the frames of the eyepiece and lenses, or disassemble the mechanical parts of the microscope - they are repaired only in special workshops.
3. Carry the microscope with both hands in a vertical position, holding the device with one hand on the tripod and the other on its base.
TERMS AND CONCEPTS YOU NEED TO LEARN
Objective, general microscope magnification.
TEST QUESTIONS
1. What elements does the optical system of a microscope consist of?
2. Do the elements of the microscope's optical system provide overall magnification?
3. What is a concave mirror used for?
4. What is the purpose of a diaphragm?
5. Is the lens turned on at the beginning of working with the microscope?
6. What is the maximum magnification that can be obtained when using the lenses and eyepiece shown in Figure 7?
7. What rules should you follow when working with a microscope?
TASKS
Carefully examine your school microscope and find all its components. Record the eyepiece and objective magnifications. Calculate the microscope magnification for each objective.Write the results in a table in your notebook.
FOR THE CURIOUS
How do you determine the size of the smallest objects that can be seen with an optical microscope?
The size of the smallest object that can be seen with the eye or magnifying device is determined by its resolution.
Resolution is the smallest distance between two points at which their images are still separated and do not merge into one. The resolution of the human eye is 200 µm (0.2 mm), of an optical microscope - 0.2 µm (0.0002 mm), of an electron microscope - 0.0002 µm (0.0000002 mm). If the size of an object is less than the resolution, then this object can no longer be considered, and vice versa. Thus, it is the resolution that determines what can be seen in a microscope and what cannot.
The value of the indicator by which the resolution of the lens is calculated is printed on its body immediately after the lens magnification indicator. It is called the lens aperture.
Behind the aperture, the resolution of the lens is calculated:
Resolution (in microns) = 0.3355 /lens aperture.
The resulting value is rounded to tenths.
Example: on a lens with a red ring (Fig. 7), the top line is marked: “4 / 0.10”. The number “4” indicates the lens magnification - four times, and “0.10” - the aperture. Resolution of this lens
it will be like this:
0.3355 / 0.10 = 3.355 « 3.4 (µm).
The study of the morphological characteristics of microbes - their shape, structure and size of cells, ability to move, etc. - is carried out using an optical device - a microscope (from the Greek “micros” - small, “skopeo” - I look). Of the biological microscopes produced, the best are MBI-1, MBI-2, MBI-3, MBR-1 and some others.
The main parts of a microscope are: the optical system (lens and eyepiece), the illuminating optical system (condenser and mirror) and the mechanical part. The optical system creates a magnified image of the object. The mechanical part ensures the movement of the optical system and the observed object (subject). The main parts of the mechanical system of a microscope (Fig. 60) are: a tripod, a stage, a tube holder with a revolver and screws for moving the tube - macrometric and micrometric.
A macrometric screw (crackle, or gear) is used for rough aiming of the microscope. The micrometer screw is a fine feed mechanism and serves for the final, precise focusing of the microscope on the specimen. A full turn of the microscrew moves the microscope tube by 0.1 mm. The micrometer screw is one of the most fragile parts of the microscope and must be handled with extreme care. The sharpest and clearest image is obtained by moving the tube using macro- and micrometer screws with appropriate lighting settings. The microscope tube is fixed in the upper part of the tripod in a tube holder. The object stage is also mounted at the top of the tripod. In modern microscopes, the stage is almost always made movable. It is driven by two screws located on both sides of the table. With the help of these screws, the specimen, together with the table, moves in different directions, which greatly facilitates the examination of the specimen at its various points. The drug is secured to the table using two terminals (clamps).
In addition to movable stages, some microscopes are equipped with cross-shaped stages. In this case, the drugs are moved in two mutually perpendicular directions. Two scales on the table allow you to mark areas of the specimen that interest the researcher, so that they can be easily found during repeated microscopy.
At the bottom of the tube holder there is a revolver with holes equipped with threads. Lenses are screwed into these holes. Objectives make up the most important and expensive part of a microscope. This is a complex system of biconvex lenses enclosed in a metal frame. Lenses magnify the subject being viewed, producing a truly magnified reverse image.
All lenses are divided into achromats and apochromats. Achromats are more common due to their simplicity and low cost. They have six lenses made of optical glass. The image obtained with achromats is sharpest in the center. The edges of the field due to chromatic aberration are often colored blue, yellow, green, red and other colors. Apochromats consist of a larger number of lenses (up to 10). For their manufacture, glass of various chemical compositions is used: boron, phosphorus, fluorite, alum. In apochromats, chromatic aberration is largely eliminated.
Typically, microscopes are equipped with three objectives, which indicate the magnification they provide: 8X (low magnification), 40X (medium magnification) and 90X (high magnification) objectives. 8X and 40X lenses are dry systems, since when working with them there is a layer of air between the drug and the lens. Rays of light, passing through media of different densities (refractive index of air n = 1, glass n = 1.52) and getting from a denser medium (glass) to a less dense one (air), are strongly deflected and do not completely enter the microscope lens. Therefore, dry lenses can only be used at relatively low magnifications (up to 500-600 times).
The higher the magnification, the smaller the diameter of the lenses. Therefore, at high magnifications, too little of the rays enter the objective lens and the image is not clear enough. To avoid this, they resort to immersion (immersion) of the lens in a medium having a refractive index close to the refractive index of glass. Such an immersion, or submersible, objective in biological microscopes is the 90X objective. When working, a drop of immersion (most often cedar) oil, the refractive index of which is 1.51, is placed between this lens and a glass slide. The lens is immersed directly in oil, light rays pass through a homogeneous system without refraction or scattering, which helps to obtain a clear image of the object in question.
An eyepiece is inserted into the upper part of the microscope tube. The eyepiece consists of two converging lenses: one facing the objective and one facing the eye. Between them in the eyepiece there is a diaphragm that blocks side rays and transmits rays parallel to the optical axis. This provides a higher contrast intermediate image. The eye lens of the eyepiece magnifies the image received from the objective. Eyepieces are manufactured with their own magnification of 7X, 10X, 15X times. The total magnification of a microscope is equal to the magnification of the objective multiplied by the magnification of the eyepiece. By combining eyepieces with objectives, various magnifications can be obtained - from 56 to 1350 times.
The condenser is a biconvex lens that collects light reflected from the mirror into a beam and directs it into the plane of the preparation, which provides the best illumination of the object. By raising and lowering the condenser, you can adjust the degree of illumination of the preparation. At the bottom of the condenser there is an iris diaphragm, through which you can also change the brightness of the lighting, narrowing it or, conversely, fully opening it.
The mirror, which has two reflective surfaces - flat and concave, is mounted on a swinging lever, with which it can be installed in any plane. The concave side of the mirror is rarely used - when working with weak lenses. The mirror reflects light rays and directs them into the lens through the condenser iris, the condenser and the object being viewed. At the bottom of the condenser frame there is a folding frame, which is used for installing light filters.
A microscope is a complex optical device; it requires careful and careful handling and appropriate operating skills. Proper care of the device and careful adherence to the instructions for use guarantee its impeccable and long-term service. Microscope image quality is highly dependent on lighting, so adjusting the lighting is an important preparatory step.
Work with a microscope can be carried out both under natural and artificial lighting. For critical work, artificial lighting is used using an OI-19 illuminator. In natural light, you need to use diffused side light rather than direct sunlight.
Modern microscopes MBI-2, MBI-3 are equipped with binocular attachments of the AU-12 type, which have their own magnification of 1.5x, and a direct replaceable tube (Fig. 61). When using a binocular attachment, microscopy is facilitated, since observation is carried out with both eyes and vision does not become tired.
There are various models of educational and research light microscopes. Such microscopes make it possible to determine the shape of microorganism cells, their size, mobility, the degree of morphological heterogeneity, as well as the ability of microorganisms to differentiate staining.
The success of observing an object and the reliability of the results obtained depend on a good knowledge of the optical system of the microscope.
Let's consider the structure and appearance of a biological microscope, model XSP-136 (Ningbo teaching instrument Co., LTD), and the operation of its components. The microscope has mechanical and optical parts (Figure 3.1).
Figure 3.1 – Design and appearance of the microscope
Mechanical part biological microscope includes a tripod with a stage; binocular attachment; coarse sharpness adjustment knob; sharpness fine adjustment handle; handles for moving the object table right/left, forward/backward; revolving device.
Optical part The microscope includes a lighting apparatus, a condenser, objectives and eyepieces.
Description and operation of the microscope components
Lenses. The lenses (achromat type) included in the microscope kit are designed for a mechanical length of the microscope tube of 160 mm, a linear field of view in the image plane of 18 mm, and a cover glass thickness of 0.17 mm. Each lens body is marked with a linear magnification, for example, 4x; 10x; 40x; 100x and, accordingly, the numerical aperture is indicated as 0.10; 0.25; 0.65; 1.25, as well as color coding.
Binocular attachment. The binocular attachment provides visual observation of the image of the object; is installed in the tripod socket and secured with a screw.
Setting the distance between the axes of the eyepieces in accordance with the eye base of the observer is carried out by turning the bodies with eyepiece tubes in the range from 55 to 75 mm.
Eyepieces. The microscope kit includes two wide-angle eyepieces with 10x magnification.
Revolving device. The four-socket revolving device ensures that the lenses are installed in the working position. Lenses are changed by rotating the corrugated ring of the revolving device to a fixed position.
Condenser. The microscope kit includes a bright-field Abbe condenser with an iris diaphragm and a filter, numerical aperture A = 1.25. The condenser is installed in a bracket under the microscope stage and secured with a screw. The brightfield condenser has an iris aperture diaphragm and a hinged frame for mounting a filter.
Lighting device. To obtain a uniformly illuminated image of objects, the microscope has an LED lighting device. The illuminator is turned on using a switch located on the rear surface of the microscope base. By rotating the lamp filament adjustment dial, located on the side surface of the microscope base to the left of the observer, you can change the brightness of the illumination.
Focusing mechanism. The focusing mechanism is located in the microscope stand. Focusing on an object is done by moving the height of the object table by rotating the handles located on both sides of the tripod. Coarse movement is carried out by a larger handle, fine movement by a smaller handle.
Subject table. The object table ensures movement of the object in the horizontal plane. The table movement range is 70x30 mm. The object is mounted on the surface of the table between the holder and the clamp of the drug guide, for which the clamp is moved to the side.
Working with a microscope
Before starting to work with drugs, it is necessary to properly set up the lighting. This allows you to achieve maximum resolution and image quality of the microscope. To work with a microscope, you should adjust the opening of the eyepieces so that the two images merge into one. The diopter adjustment ring on the right eyepiece should be set to “zero” if the visual acuity of both eyes is the same. Otherwise, it is necessary to perform general focusing, then close the left eye and achieve maximum sharpness for the right one by rotating the correction ring.
It is recommended to start studying the drug with a lens of the lowest magnification, which is used as a search lens when choosing an area for more detailed study, then you can move on to working with stronger lenses.
Make sure the 4x lens is ready for use. This will help you position the slide in place and also position the object to be examined. Place the slide on the stage and gently clamp it using the spring holders.
Connect the power cord and turn on the microscope.
Always start your study with a 4x lens. To achieve clarity and sharpness of the image of the object under study, use the coarse and fine focusing knobs. If the weak 4x objective produces the desired image, rotate the nosepiece to the next higher 10x setting. The revolver should lock into place.
While viewing the object through the eyepiece, turn the (large diameter) coarse focusing knob. To get the clearest image, use the (small diameter) focus knob.
To control the flow of light passing through the condenser, you can open or close the iris diaphragm located under the stage. By changing the settings, you can achieve the clearest image of the object under study.
When focusing, do not allow the lens to come into contact with the object of study. When the lens is magnified up to 100x, the lens is very close to the slide.
Rules for handling and caring for a microscope
1 The microscope must be kept clean and protected from damage.
2 To maintain the appearance of the microscope, it must be periodically wiped with a soft cloth lightly soaked in acid-free petroleum jelly, after removing dust, and then wiped with a dry, soft, clean cloth.
3 Metal parts of the microscope must be kept clean. To clean the microscope, use special non-corrosive lubricants.
4 To protect the optical parts of the visual attachment from dust, it is necessary to leave the eyepieces in the eyepiece tubes.
5 Do not touch the surfaces of optical parts with your fingers. If dust gets on the lens, remove the dust using a fan or brush. If dust has penetrated inside the lens and a cloudy coating has formed on the inner surfaces of the lenses, you must send the lens to an optical workshop for cleaning.
6 To avoid misalignment, it is necessary to protect the microscope from shocks and impacts.
7 To prevent dust from getting on the inner surface of the lenses, the microscope must be stored under a cover or in packaging.
8 You should not disassemble the microscope and its components yourself to troubleshoot problems.
Security measures
When working with a microscope, the source of danger is electric current. The design of the microscope eliminates the possibility of accidental contact with live parts that are energized.
