The device of the microscope, the structure of the 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. If we give a more precise definition, then a microscope is an optical instrument ( with one or more lenses) used to obtain enlarged images of some objects that are not visible to the naked eye.
Eg, microscopes, used in today's schools, are able to magnify 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 a rather long path of discoveries, and even disappointments.
The 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, giving an image magnification several times. I will clarify that the very first lenses were not made of glass, but of some kind of transparent stone, so there is no need to talk about image quality.
In the future, have already been invented microscopes consisting of two lenses. The first lens is the lens, it addressed the object under study, and the second lens is the eyepiece through which the observer looked. But the image of objects was still strongly distorted, due to strong spherical and chromatic deviations - the light was refracted unevenly, and because of this, the picture was fuzzy 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 physicists such as Amici, Fraunhofer, and others. A complex system consisting of converging and diverging lenses was already used in the lens design. Moreover, these lenses were made of different types of glass, which compensated for the shortcomings of each other.
Microscope scientist from Holland, Leeuwenhoek already had an object table, where all the studied objects were folded, and there was also a screw that allowed this table to be moved smoothly. Then a mirror was added - for better illumination of objects.
The structure of the microscope
There are simple and compound microscopes. A simple microscope is a single lens system, just like an ordinary magnifying glass. A complex microscope, on the other hand, combines two simple lenses. Difficult microscope, respectively, gives a greater increase, and besides, it has a higher resolution. It is the presence of this ability (resolving) that makes it possible to distinguish the details of the samples. An enlarged image, where details cannot be distinguished, will give us some useful information.
Compound 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 enlarged by another lens system ( eyepiece), it is placed, directly, closer to the eye of the observer. These 2 lens systems are located at opposite ends of the microscope tube.
Modern microscopes
Modern microscopes can give a colossal magnification - up to 1500-2000 times, while the image quality will be excellent. Binocular microscopes are also quite popular, in which the image from one lens is split in two, while you can look at it with two eyes at once (in two eyepieces). This allows you to even much better distinguish visually small details. Similar microscopes are commonly used in different laboratories ( including in medical) for research.
Electron microscopes
Electron microscopes help us "see" images of individual atoms. True, the word “consider” is used here relatively, since we do not look directly with our eyes - the image of the object appears as a result of the most complex processing of the received data by the computer. The device of a microscope (electronic) is based on physical principles, as well as the method of “feeling” the surfaces of objects with the thinnest needle, in which the tip is only 1 atom thick.
USB microscopes
At present, during the development of digital technologies, each person can purchase a lens attachment for the camera of his 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 a monitor.
Most digital cameras are capable of taking pictures in macro photography, with it you can take a photo of the smallest objects. And if you place a small converging lens in front of your camera lens, you can easily get a photo magnification up to 500x.
Today, new technologies help to see what was literally inaccessible a hundred years ago. Parts microscope throughout its history, they have been constantly improved, and at present we see the microscope already 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 how to use a microscope correctly:
MICROSCOPE. MICROSCOPIC INSTRUMENTS.
Microscopic technique.
The main stages of cytological and histological analysis:
The choice of the object of study
Preparing it for examination under a microscope
Application of microscopy methods
Qualitative and quantitative analysis of the obtained 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, experimental and pathological conditions.
Light microscope. A microscope is an optical device designed to obtain enlarged images of biological objects and details of their structure that are not visible to the naked eye.
The 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, object stage, macro- and micro-screw mechanisms, condenser movement mechanism
Optical parts of the microscope.
Lens- the main optical part of the microscope, which creates an image of the preparation. The lens is a system of lenses in a metal frame, where they distinguish between the front - the main or magnifying lens closest to the object, which builds the image and the correction - they eliminate the aberrations of the front lens. Lenses are divided into:
A) by 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) for 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); plan monochromats, plan achromats, plan apochromats (image surface curvature corrected),
C) according to the properties for dry-air and immersion. When using dry-air lenses, there is an air space between the preparation and the lens, while 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. Maximum magnification is only possible with an immersion objective (usually a 90 magnification objective). Immersion objectives are designed to work with coverslips no thicker than 0.17 mm.
Eyepiece- the optical system used to view the image built by the lens. A simple eyepiece (Huygens) consists of two plano-convex lenses facing the objective with their convex surface. Between the lenses is a fixed aperture diaphragm. An arrow is attached to the diaphragm - a pointer. The upper lens is called the eye lens, and the magnification of the eyepiece is indicated on its frame. The lower lens is called the field lens. The eyepiece usually magnifies the image by 5-25 times
Mirror- directs the flow of light through the condenser to the drug. It has a flat and concave surface, which are used depending on the degree of illumination.
Condenser- collects light rays and focuses them on the preparation, providing sufficient and uniform illumination of the latter. The condenser consists of two lenses: the lower biconvex and the upper plano-convex. With the help of a condenser, the degree of illumination of the object under study is regulated.
Topic 1. CELL
§6. STRUCTURE OF THE MICROSCOPE
you familiarize yourself with structure microscope and learn how to calculate its magnification.
Will we work with a microscope?
What can be seen through a microscope other than bacteria?
Microscope (from the Greek "micros" - small and "skopeo" - look, consider) - where is a magnifying device that allows you to examine an object and 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. (ml. 6). With the right settings, a school microscope allows you to see not only the cell, but also its individual internal structures. And if you have some experience - even perform some interesting experiments.
The microscope consists of a body and elements of the optical system through which light passes.
The body parts are:
✓ foundation;
Rice. V. Appearance and main components of a school microscope
✓ the subject table, on which the prototype is placed, is fixed on the table with the help of two flexible holders;
In a tripod with a variable angle, on which there is a large coarse adjustment screw (macro screw) and a smaller fine adjustment screw (micro screw);
✓ a tube, on the lower part of which a revolving nozzle 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 under the subject table;
✓ revolver attachment with lenses of different magnification;
✓ eyepiece through which the object of study is observed.
The mirror is used to adjust the best illumination of the preparation. The aperture controls the contrast and brightness of the image: if the aperture is closed, the image is very contrasting, but dark; if the aperture is fully open, then the contrast is small, and there is a lot of light, so the image is overbright.
Rice. 7. Objectives (a), eyepiece (b) of a school microscope and their marking
Objects. The school microscope has three lenses: very small (4x), small (10x) and large (40x) magnification. For easy change, they are screwed into the turret. 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 turn on another lens in the optical system, a slight click is heard - this triggers the spring lock of the turret.
The lens is the main element of the optical system of the microscope. On the lens, the numbers indicate its technical characteristics.
In the top line, the first digit indicates the magnification of the lens (p. 7).
The product of the objective magnification and the magnification of the eyepiece gives the total magnification of the microscope. For example, with a 4x objective and a 10x eyepiece enabled, the total magnification of the microscope is: 4 ∙ 10 = 40 (times).
When working with a microscope, a prototype is placed on the object table, fixed with holders, and a low magnification lens (10x) is turned on. By rotating the mirror, light is directed to the preparation, and macroscrew adjust the clarity. Then, if necessary, turn on the high-magnification lens, adjust the clarity with a micro-screw and contrast the image with a diaphragm.
When working with a microscope, follow these rules:
1. Lenses of eyepieces and objectives must be protected from contamination and mechanical damage: do not touch with fingers and hard objects, do not allow water and other substances to get on them.
2. It is forbidden to unscrew the frames of the eyepiece and objectives, disassemble the mechanical parts of the microscope - they are repaired only in special workshops.
3. It is necessary to carry the microscope with both hands in a vertical position, holding the device with one hand on the tripod, and with the other - on its base.
TERMS AND CONCEPTS TO LEARN
Objective, general magnification of the microscope.
CONTROL QUESTIONS
1. What elements does the optical system of a microscope consist of?
2. Do the elements of the optical system of the microscope provide an overall magnification?
3. What is a concave mirror used for?
4. What is the purpose of the diaphragm?
5. Is the lens turned on at the beginning of work with the microscope?
6. What is the maximum magnification that can be obtained by using the lenses and eyepiece shown in Figure 7?
7. What rules should be followed when working with a microscope?
TASKS
Take a close look at your school microscope, find all its components. Record the eyepiece and objective magnifications. Calculate the magnification of the microscope for each objective.Record the results in a table in your notebook.
FOR INQUIRY
How to determine the size of the smallest objects that can be seen in an optical microscope?
The size of the smallest object that can be seen with the eye or a magnifying instrument 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 microns (0.2 mm), the optical microscope - 0.2 microns (0.0002 mm), the electron microscope - 0.0002 microns (0.0000002 mm). If the size of the object is less than the resolution, then this object can no longer be considered, and vice versa. Thus, it depends on the resolution what can be seen through a microscope and what cannot.
The value of the indicator, by which the resolution of the lens is calculated, is marked on its body immediately after the magnification indicator of the lens. It is called the lens aperture.
Behind the aperture, the resolution of the lens is calculated:
Resolution (in µm) = 0.3355 / lens aperture.
The resulting value is rounded to tenths.
Example: A lens with a red ring (Fig. 7) has the marking “4 / 0.10” in the top line. The number "4" indicates the magnification of the lens - four times, and "0.10" - the aperture. Resolution of this lens
will be like this:
0.3355 / 0.10 \u003d 3.355 "3.4 (μm).
The study of the morphological features of microbes - their shape, structure and size of cells, the ability to move, etc. - is carried out using an optical device - a microscope (from the Greek "micros" - small, "scopeo" - 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 the microscope: optical system (objective and eyepiece), illumination optical system (condenser and mirror) and mechanical part. The optical system creates an enlarged image of the object. The mechanical part ensures the movement of the optical system and the observed object (object). The main parts of the mechanical system of the microscope (Fig. 60) are: a tripod, an object stage, a tube holder with a revolver and screws for moving the tube - macrometric and micrometric.
The macrometric screw (kremalier, or cog) is used for coarse 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 a 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 the appropriate lighting setting. The tube of the microscope is fixed in the upper part of the tripod in the tube holder. The object table is also fixed 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 preparation, together with the table, moves in different directions, which greatly facilitates the examination of the preparation at its various points. The drug is fixed on the table with two terminals (clamps).
In addition to movable tables, some microscopes are equipped with cruciform tables. In this case, the preparations are moved in two mutually perpendicular directions. Two scales on the table allow you to mark areas of interest to the researcher of the drug, so that they can be easily found during repeated microscopy.
At the bottom of the tube holder there is a revolver with threaded holes. Objectives are screwed into these holes. Objectives are the most important and expensive part of a microscope. This is a complex system of biconvex lenses enclosed in a metal frame. Objectives magnify the object being viewed, giving a true magnified inverse image.
All lenses are divided into achromats and apochromats. Achromats are more common due to their simplicity and cheapness. 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 in 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: boric, phosphoric, fluorite, alum. Chromatic aberration has been largely eliminated in apochromats.
Usually microscopes are supplied with three objectives, which indicate the magnification they give: objectives 8X (low magnification), 40X (medium magnification) and 90X (high magnification). Objectives 8X and 40X are dry systems, as there is a layer of air between the preparation and the objective when working with them. Rays of light passing through media of different density (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 fall into 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 lenses should be. 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 with a refractive index close to that of glass. Such an immersion, or submersible, objective in biological microscopes is the 90X objective. When working between this lens and a glass slide, a drop of immersion (most often cedar) oil is placed, the refractive index of which is 1.51. The lens is immersed directly in oil, light rays pass through a homogeneous system without being refracted or scattered, which helps to obtain a clear image of the object in question.
An eyepiece is inserted into the top of the microscope tube. The eyepiece consists of two converging lenses: one facing the objective and the other facing the eye. Between them in the eyepiece there is a diaphragm that delays 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 made with their own magnification of 7X, 10X, 15X times. The total magnification of a microscope is equal to the magnification of the objective and the magnification of the eyepiece. When combining eyepieces with objectives, various magnifications can be obtained - from 56 to 1350 times.
The condenser is a biconvex lens that collects the light reflected from the mirror into a beam and directs it into the preparation plane, which provides the best illumination of the object. By raising and lowering the condenser, you can adjust the degree of illumination of the drug. At the bottom of the condenser is an iris diaphragm, through which you can also change the brightness of the light, narrowing or, conversely, fully opening it.
The mirror, which has two reflective surfaces - flat and concave, is mounted on a rocking 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 to the lens through the iris diaphragm of the condenser, the condenser and the object in question. At the bottom of the condenser frame there is a folding frame, which serves to install light filters.
A microscope is a complex optical device, it requires careful and careful handling, appropriate skills in work. Proper care of the device and careful observance of the rules of use guarantee the perfect and long service life of the device. The quality of the image in a microscope is highly dependent on illumination, so setting the illumination is an important preparatory operation.
Work with a microscope can be carried out both in natural and artificial light. For responsible work, they use artificial lighting, using the OI-19 illuminator. In natural light, you need to use diffused side light, and not direct sunlight.
Modern microscopes MBI-2, MBI-3 are equipped with binocular attachments of the AU-12 type, which have an intrinsic magnification of 1.5x, and a straight interchangeable tube (Fig. 61). When using a binocular attachment, microscopy is facilitated, since observation is made with both eyes and vision is not 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.
Consider the device and appearance of a biological microscope, model XSP-136 (Ningbo teaching instrument Co., LTD), the operation of its components. The microscope has mechanical and optical parts (Figure 3.1).
Figure 3.1 - Device and appearance of the microscope
Mechanical biological microscope includes a tripod with a subject table; binocular head; coarse adjustment knob for sharpness; fine adjustment knob for sharpness; handles for moving the object stage to the right / left, forward / backward; revolver device.
Optical part The microscope includes a lighting apparatus, a condenser, objectives and eyepieces.
Description and operation of the components of the microscope
Lenses. The objectives (achromatic type) supplied with the microscope 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 slip thickness of 0.17 mm. The body of each lens is marked with a linear magnification, for example, 4x; 10x; 40x; 100x and, accordingly, a numerical aperture of 0.10 is indicated; 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; mounted on a 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 housings with eyepiece tubes in the range from 55 to 75 mm.
Eyepieces. The microscope comes with two wide-angle eyepieces with a magnification of 10x.
Revolving device. A four-socket revolving device ensures the installation of lenses in the working position. Change of lenses is made by rotation of the corrugated ring of the revolving device to a fixed position.
Condenser. The microscope kit includes an Abbe bright-field condenser with an iris diaphragm and a filter, numerical aperture A=1.25. The condenser is mounted in a bracket under the microscope stage and secured with a screw. The bright field condenser has an iris aperture diaphragm and a hinged frame for installing a light filter.
Lighting device. To obtain a uniformly illuminated image of objects in the microscope, there is an illumination LED device. The illuminator is turned on using a switch located on the rear surface of the microscope base. By rotating the lamp incandescence 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.
focus mechanism. The focusing mechanism is located in the microscope stand. Focusing on the object is carried out by moving the object stage along the height by rotating the handles located on both sides of the tripod. Coarse movement is carried out with a larger handle, fine movement with a smaller handle.
Subject table. The object table provides movement of the object in the horizontal plane. The table movement range is 70x30 mm. The object is fixed on the surface of the table between the holder and the clamp of the preparation driver, for which the clamp is moved to the side.
Working with a microscope
Before starting work with preparations, it is necessary to properly adjust 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 a general focusing, then close the left eye and achieve maximum sharpness for the right by rotating the correction ring.
It is recommended to start the study of the preparation with the lens of the smallest magnification, which is used as a search one when choosing a site for a more detailed study, then you can proceed to work with stronger lenses.
Make sure the 4x lens is ready to go. This will help you set the slide in place and also position the object for examination. Place the slide on the stage and carefully clamp it with the spring holders.
Connect the power cord and turn on the microscope.
Always start your survey with a 4x objective. To achieve clarity and sharpness of the image of the object under study, use the coarse and fine focus knobs. If the desired image is obtained with a weak 4x objective, rotate the turret to the next higher value of 10x. The revolver should lock into position.
While observing an object through the eyepiece, turn the coarse focus knob (large diameter). Use the fine focus knob (small diameter) to get the clearest image.
To control the amount 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.
During focusing, do not allow the lens to come into contact with the object of study. When the objective is magnified up to 100x, the objective is very close to the slide.
Handling and Care of the Microscope
1 The microscope must be kept clean and protected from damage.
2 To preserve the appearance of the microscope, it must be periodically wiped with a soft cloth slightly soaked in acid-free vaseline, after removing dust, and then wiped with a dry, soft, clean cloth.
3 The metal parts of the microscope must be kept clean. Special lubricating non-corrosive liquids should be used to clean the microscope.
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 there is dust on the objective lens, it should be removed with a blower or a brush. If dust has penetrated inside the lens and a cloudy coating has formed on the inner surfaces of the lenses, it is necessary to send the lens for cleaning to an optical workshop.
6 To avoid misalignment, protect the microscope from shocks and impacts.
7 To prevent dust from getting on the inside of the lenses, the microscope should be stored under a case or in its packaging.
8 Do not disassemble the microscope and its components for troubleshooting.
Security measures
When working with a microscope, a source of danger is electric current. The design of the microscope eliminates the possibility of accidental contact with live parts under voltage.
