The device of the microscope is its main parts. The structure of the microscope. Subspecies of light microscopes

The first concepts of a microscope are formed at school in biology lessons. There, children will learn in practice that with the help of this optical device it is possible to examine small objects that cannot be seen with the naked eye. The microscope, its structure is of interest to many schoolchildren. The continuation of these interesting lessons for some of them is the whole further adult life. When choosing some professions, it is necessary to know the structure of the microscope, since it is the main tool in the work.

The structure of the microscope

The device of optical devices complies with the laws of optics. The structure of a microscope is based on its constituent parts. Units of the device in the form of a tube, an eyepiece, an objective, a stand, a table for the location of the object of study, an illuminator with a condenser have a specific purpose.

The stand holds the tube with the eyepiece, objective. An object table with an illuminator and a condenser is attached to the stand. An illuminator is a built-in lamp or mirror that serves to illuminate the object under study. The image is brighter with an illuminator with electric lamp. The purpose of the condenser in this system is to regulate the illumination, focusing the rays on the object under study. The structure of microscopes without condensers is known; a single lens is installed in them. IN practical work it is more convenient to use optics with a movable table.

The structure of the microscope, its design directly depend on the purpose of this device. For scientific research, X-ray and electronic optical equipment is used, which has a more complex device than light devices.

The structure of a light microscope is simple. These are the most accessible optical devices, they are most widely used in practice. An eyepiece in the form of two magnifying glasses placed in a frame, and an objective, which also consists of magnifying glasses tucked into a frame, are the main components of a light microscope. This entire set is inserted into a tube and attached to a tripod, in which is mounted an object table with a mirror located under it, as well as an illuminator with a condenser.

The main principle of operation of a light microscope is to enlarge the image of the object of study placed on the object table by passing light rays through it with their further contact with the lens system of the objective. The same role is played by the eyepiece lenses used by the researcher in the process of studying the object.

It should be noted that light microscopes are also not the same. The difference between them is determined by the number of optical blocks. There are monocular, binocular or stereo microscopes with one or two optical units.

Despite the fact that these optical devices have been used for many years, they remain incredibly in demand. Every year they improve, become more accurate. The last word has not yet been said in the history of such useful instruments as microscopes.

bright field microscopy

The study of microorganism cells invisible to the naked eye, the size of which does not exceed tens and hundreds of micrometers (1 μm = 0.001 mm), is possible only with the help of microscopes (from the Greek. mikros- small, skopeo- I'm watching). These devices make it possible to obtain hundreds of times (light microscopes) and tens to hundreds of thousands of times (electron microscopes) an enlarged image of the objects under study.

Using a microscope, they study the morphology of microorganism cells, their growth and development, and carry out primary identification (from lat. identity- identification) of the studied organisms, monitor the nature of the development of microbial cenoses (communities) in the soil and other substrates.

The microscope consists of two parts: mechanical (auxiliary) and optical (main).

The mechanical part of the microscope. It includes a tripod, an object table and a tube (pipe).

Tripod has a base in the form of a horseshoe and a column (tube holder) in the form of an arc. A box of mechanisms adjoins it, a system of gears for regulating the position of the tube. The system is driven by the rotation of macrometric and micrometric screws.

micrometer screw(kremalera, gear, macro screw) serves for preliminary orientation of the image of the object in question.

micrometer screw(microscrew) is used for subsequent clear focusing. When the microscrew is fully turned, the pipe moves 0.1 mm (100 µm).

Turning the screws clockwise lowers the tube towards the specimen, while turning it counterclockwise raises it away from the specimen.

The subject table is used to place the drug with the object of study on it. The object table rotates and moves in mutually perpendicular planes with the help of screws. In the center of the table there is a round hole for illuminating the preparation from below with light rays directed by the microscope mirror. Two clamps are built into the table (terminals)- springy metal plates designed to fix the drug.

If it is necessary to examine the surface of the preparation without allowing gaps (which is important when counting), or if during the work it is required to re-examine any specific area on the preparation, the object table will be placed drug parent. It has a system of rulers - verniers, with which you can assign coordinates to any point of the object under study. To do this, when installing the preparation-giver, the center of rotation of the stage and the optical axis of the microscope system should be aligned with the centering plate of the preparation-giver (hence the object table with the preparation-giver is sometimes called cruciform).

Tube (pipe)- frame, which contains the elements of the optical system of the microscope. A revolver (objective holder) with sockets for lenses is attached to the bottom of the tube. Modern models microscopes have an inclined tube with an arcuate tube holder, which ensures the horizontal position of the stage.

Optical part of the microscope consists of the main optical unit (objective and eyepiece) and auxiliary lighting system (mirror and condenser). All parts of the optical system are strictly centered relative to each other. In many modern microscopes, the mirror and condenser are replaced by an adjustable light source built into the instrument.

Lighting system located under the subject table. Mirror reflects incident light into a condenser . One side of the mirror is flat , another - concave. When working with a condenser, only a flat mirror must be used. A concave mirror is used when working without a condenser with low magnification lenses. . Condenser(from lat . condenso- condense, thicken), consisting of 2-3 short-focus lenses, collects the rays coming from the mirror , and direct them to the object. The condenser is necessary, first of all, when working with an immersion system. The condenser lenses are mounted in a metal frame connected to a gear mechanism that allows the condenser to be moved up and down with a special screw. To adjust the intensity of illumination in the condenser there is iris(petal) diaphragm, made of sickle-shaped steel plates

Stained preparations are best viewed with an almost fully open diaphragm, unstained - with a reduced aperture of the diaphragm. .

Below the condenser is ring holder for light filters (usually blue and white frosted glass). When working with an artificial light source, filters give the impression of daylight , which makes microscopy less tiring for the eyes.

Lens(from lat. objectum- subject) - the most important part of the microscope. This is a multi-lens short-focus system, the quality of which mainly determines the image of the object. The outer lens facing the preparation with its flat side is called the frontal lens. It is she who provides an increase . The remaining lenses in the lens system perform mainly the functions of correcting optical imperfections that occur when examining objects. .

One of these shortcomings is the phenomenon spherical aberration. It is associated with the property of lenses to refract peripheral and central rays unevenly. The former are usually refracted to a greater extent than the latter, and therefore intersect at a closer distance to the lens. As a result, the image of the point takes the form of a blurry spot.

Chromatic aberration occurs when a beam of rays of different wavelengths passes through the lens . Refracted in different ways , Rays do not intersect at the same point. Short wavelength blue-violet rays are more refracted than longer wavelength red ones. As a result, a colorless object appears color.

Lenses that eliminate spherical and partial chromatic aberration include achromats. They contain up to 6 lenses and correct the primary spectrum (yellow-green part of the spectrum) without eliminating the secondary spectrum. The image obtained with the help of achromats is not colored, but its edges have a red or bluish halo. In modern achromats, this drawback is almost imperceptible. best material for lenses of achromats - flint glasses - old grades of glass with a high content of lead oxide.

Lenses that eliminate chromatic aberration and for the secondary spectrum are called apochromats. They may contain from 1 to 12 lenses. Apochromat lenses for better correction of the secondary spectrum are made of fluorspar, rock salt, alum and other materials. Apochromats make it possible to eliminate coloring of an object and obtain an equally sharp image from rays different color. The maximum effect when working with apochromats can only be achieved when they are combined with compensating eyepieces that compensate for the optical imperfections of the objectives. In compensating eyepieces, the chromatic error is the opposite of the objective chromatic error, and as a result, the chromatic aberration of the microscope is almost completely compensated for.

Planachromats - a variety of apochromats with a flat field of view. Planachromat lenses completely eliminate the curvature of the field of view, which causes uneven focusing of the object (with the curvature of the field of view, only part of the field is focused). Planachromats and planapochromats are used in microphotography.

Lenses are dry and submersible (immersion). At work with dry There is air between the front lens of the objective and the object of study. Optical calculation immersion lenses provides for their operation when the front lens of the objective is immersed in a liquid homogeneous medium. When working with a dry lens, due to the difference between the refractive indices of glass (1.52) and air (1.0), part of the light rays is deflected and does not enter the observer's eye (Fig. 1).

When working with an immersion objective, it must be placed between the cover slip and objective lenses. cedar

oil, whose refractive index is close to that of glass (Table 1).

Rays in an optically homogeneous homogeneous medium do not change their direction. Immersion lenses on the frame have a black circular cut and designations: I - immersion (immersion), HI - homogen immersion (homogeneous immersion), OI - oil immersion, MI - oil immersion. Lenses are distinguished by their magnification.

Lens native magnification (V) determined by the formula

Where l- optical length of the tube or the distance between the focal plane of the lens and the image plane, which is 128-180 mm for different lenses; f- focal length of the lens: the longer it is, the smaller the magnification of the lens.

The magnification of lenses is indicated on their frame (8x, 40x, 9x). Each lens is characterized, in addition, by a certain value of the working distance in millimeters.

In lenses with low magnification, the distance from the front lens of the objective to the preparation is greater than in lenses with high magnification. So, lenses with a magnification of 8 x, 40 x and 90 x have a working distance of 13.8, respectively; 0.6 and 0.12 mm. Depending on which lens you are working with, a macrometric and micrometric screw is selected to focus it. An immersion lens has a working distance of 0.12 mm to the lens, which is why it is often referred to as "myopic".

1 Cedar oil is obtained from the seeds of virgin juniper Juniperus virginiana or Zeravshan juniper Juniperus seravschana. At present, as an immersion liquid, synthetic products are more often used, which correspond in optical properties to cedar oil.

Microscope (from the Greek mikros - small and skopeo - I look) is optical instrument designed for visual examination of small objects invisible to the naked eye. In microbiology, a wide variety of microscopes are used, which have different designs and devices, but are similar to each other in their main elements.

Rice. 33. Microscope device

1 - tripod; 2 - tube; 3 - head; 4 - subject table; 5 - macro screw; 6 - microscrew;

7 - condenser; 8 - lighting device; 9 - lens; 10 - eyepiece.

The microscope consists of two main parts: mechanical And optical(Fig. 33). The mechanical part of the microscope includes a tripod (1), which consists of a massive base and a tube holder.

In the upper part of the tube holder, a monocular or binocular tube (2) and a head with a guide of the " dovetail» (3). A revolver is placed on this guide. The revolver has four threaded holes for screwing in lenses and a lock for centering them. The spherical part of the revolver rotates on balls (for quick lens change) and is equipped with a ball lock.

In the middle part of the tube holder there is an object table (4), which has clamps for fixing the glass slide and side screws for longitudinal and transverse movement. This greatly facilitates the work with the preparation and allows you to view the object at its various points. There is a hole in the center of the stage for light to pass through. Some research microscopes are equipped with additional micro-blades for micro-movement of the object.

The tube holder in the lower part carries a guide with large handles (5) for coarse focusing of the microscope (macrometric screw or rack) and small handles (6) or a disk for fine focusing of the microscope (micrometric screw). By rotating the rack, a rough, visible to the eye, vertical movement of the object stage or tube is produced. With the help of a micrometer screw, the object stage or tube is moved up and down a very small distance, noticeable only during microscopy. One turn of the micrometer screw gives a movement of 0.1 mm. This is enough to accurately focus the subject. To avoid breakage of the micrometer screw, do not make more than 1-1.5 turns with it.

Optical part The microscope includes an illumination system and a lens system.

Lighting the system is located under the object stage and consists of a condenser (7) and an illumination device (8). The condenser is the most important part of the microscope, on which the success of microbiological research depends. It is designed to collect scattered light rays, which, passing through the lenses of the condenser, are collected in focus on the plane of the preparation under consideration.

The condenser is fixed with a ring in the frame, located on the bracket, and is held by a small bolt. In addition, there is a special side screw that allows you to move the condenser up and down by 20 mm to change the illumination of the field of view. There is an iris diaphragm at the bottom of the condenser. The aperture opening is adjusted by a special lever, which makes it possible to change the brightness of the illumination of the object. In the lower part of the condenser there is a movable frame (frame), in which light filters made of frosted or blue glass are placed. Light filters are used to reduce the degree of illumination and improve the clarity of the image.

Light rays are directed into the condenser using a mirror or a special electric lighting device, which has its own design features for various microscopes.

The most important part of the microscope is also system lens, which creates an enlarged inverse and virtual image of the object. It consists of an objective (9) located in the lower part of the tube and aimed at the object under study, and an eyepiece (10) placed in the upper part of the tube.

Lens is a metal cylinder in which the lenses are fixed. The main (frontal) lens is directed to the preparation. Only it provides the necessary increase in the imaged object, all the rest correct the image and are called correction. The resolution of the microscope depends on the front lens, i.e. the smallest distance at which two closely spaced points can be distinguished separately. In modern optical microscopes, the resolution of the objectives is 0.2 µm. The greater the curvature of the front lens, the more degree its increase.

However, the frontal lens also causes negative phenomena that interfere with the study, the main of which are spherical aberration and chromatic aberration.

Spherical aberration is due to the fact that the side rays incident on the edges of the front lens are refracted more strongly than the others and make the image of the object blurry, fuzzy. Therefore, each point of the object looks like a circle. To correct the shortcomings of the front lens in lenses - achromats there is a system of corrective lenses (from 3-4 to 10-12).

Being the simplest, achromats suffer from chromatic aberration. Chromatic aberration is caused by the decomposition of a beam of white light passing through a frontal lens into its component parts of the spectrum. The image of the object is obtained as if surrounded by a rainbow. Glass lenses refract blue-violet rays most strongly and red ones least of all.

The elimination of spherical and chromatic aberration is most fully achieved using apochromats. They consist of a set of lenses having different curvatures and made from different types of glass. This creates the conditions for ensuring the clarity of the image and for a more correct transmission of the coloring of colored objects.

At first they used achromats, which allowed to eliminate chromatic aberration in relation to the two brightest colors of the spectrum. Therefore, the image of the object was devoid of color. Subsequently, special types of glass were obtained, the lenses of which not only eliminated the coloring of the object, but also gave a clear image from rays of different colors. Such lenses are called apochromats.

panachromats have an even more complex design and allow you to create sharper contours of objects throughout the field of view

To select lenses, the designations are engraved on their body: achr. - achromat, apo. - apochromat; pan. - panchromat

Distinguish lenses dry and immersion. When using a dry lens, there is a layer of air between its front lens and the object in question. Light rays from the air pass through the preparation glass, then again through air layer, as a result of which they are refracted and scattered at the boundary of dissimilar media. After such transitions through heterogeneous media, only a part of the light rays penetrates the lens. To capture the maximum amount of light rays, the front lens of the objectives must have a relatively large diameter, large focal length and low curvature. Therefore, dry lenses have a small degree of magnification (8x, 10x, 20x, 40x).

To achieve a higher magnification, it is necessary to create a homogeneous optical medium between the front lens of the objective and the preparation. This becomes possible when the lens is immersed in a drop of cedar oil, which is applied to the preparation. Cedar oil has a refractive index n = 1.515, close to the refractive index of the drug glass (n = 1.52). Therefore, the light rays passing through the immersion oil do not scatter and, without changing their direction, enter the lens, providing a clear view of the object under study. In the absence of cedar oil, substitutes are used: peach oil (n = 1.49); Castor oil(1.48-1.49); clove oil (1.53); immersiol, which includes peach oil (50 g), rosin (10 g), naphthalene (10 g), salol (1 g); a mixture of equal volumes of castor (n = 1.47) and dill (n - 1.52) oils.

Oil immersion lenses are marked “MI”, a black strip on the cylinder and a sinking front lens, which protects it from damage in case of careless contact of the lens with the preparation. The degree of magnification for oil immersion lenses can be 80 x, 90 x, 95 x, 100 x and 120 x.

Water immersion lenses have a magnification of 40X. They are marked with the letters "VI" and a white stripe on the cylinder. Such objectives are very sensitive to changes in the thickness of the coverslip, since the refractive index of water differs from that of glass. The best image quality is observed when using coverslips with a thickness of 0.17 mm.

Most microscopes are equipped with three types of objectives (10x, 20x, 40x, and 90x), providing respectively low, medium, and high magnification. The smallest magnification of the lens is 8 x. When the lens is treated with acetone or gasoline for a long time to remove immersion oil, the adhesive that connects the lenses is destroyed. This renders the optical system of the lens unusable.

Eyepiece located at the top of the tube and magnifies the image given by the lens. It consists of two plano-convex lenses: the upper lens (eye) and the lower, facing the object, collecting lenses. The researcher's eye, as if continuing the optical system of the microscope, refracts the rays coming out of the eyepiece and builds an enlarged image of the object on the retina.

Both lenses are enclosed in a metal frame. A number is engraved on the frame of the eyepieces, showing how many times the eyepiece increases the magnification of the objective. A monocular microscope uses one lens, while a binocular microscope uses two. Accordingly, the image of the object is flat or stereoscopic. The binocular tube can be adjusted to any interpupillary distance in the range from 55 to 75 cm.

The magnification of the eyepiece is indicated on the metal frame of the eye lens (7 x, 10 x or 15 x). The total magnification of a microscope is equal to the product of the magnification factor of the objective and the magnification factor of the eyepiece. Thus, the smallest magnification of biological microscopes is 56 times (8 is the magnification of the objective, multiplied by 7 is the magnification of the eyepiece), and the largest - 1800 (120x15).

However, an enlarged image of an object may or may not be sharp. The clarity of the image is determined by the resolution of the microscope (useful magnification) i.e. the minimum distance between two points before they merge into one. The higher the resolution of the microscope, the smaller the object can be seen.

The resolving power of a microscope depends on the wavelength of the light used and the sum of the numerical apertures of the objective and the condenser:

where α is the minimum distance between two points;

A 1 - numerical aperture of the lens;

A 2 - numerical aperture of the condenser;

λ is the wavelength of the light used.

The numerical apertures of the objective and condenser are indicated on their bodies. The resolution of a microscope can be increased by using ultraviolet irradiation. However, ultraviolet microscopes are very expensive, making them difficult to use. Most often, an immersion system is used to increase the resolution of a microscope.

→

The design of the microscope directly depends on its purpose. As you probably already guessed, microscopes are different, and an optical microscope will differ significantly from an electron or X-ray microscope. This article will discuss in detail the structure optical light microscope, which is currently the most popular choice of amateurs and professionals, and with which you can solve many research problems.

Optical microscopes also have their own classification and may differ in their structure. However, there is a basic set of parts that go into any optical microscope. Let's look at each of these details.

In a microscope, optical and mechanical parts can be distinguished. The optics of a microscope includes objectives, eyepieces, and a lighting system. A tripod, a tube, an object table, fastenings of the condenser and light filters, mechanisms for adjusting the object table and the tube holder constitute the mechanical part of the microscope.

Let's start with perhaps optical part .

• Eyepiece. That part of the optical system that is directly connected with the eyes of the observer. In the simplest case, the lens consists of a single lens. Sometimes, for greater convenience, or, as they say, "ergonomics", the lens can be equipped, for example, with an "eyecup" made of rubber or soft plastic. Stereoscopic (binocular) microscopes have two eyepieces.
• Lens. Perhaps the most important part of the microscope, providing the main magnification. The main parameter is aperture, what it is is described in detail in the "Basic parameters of microscopes" section. Objectives are divided into "dry" and "immersion", achromatic and apochromatic, and even in cheap simple microscopes they are a rather complex lens system. Some microscopes have unified lens mounting elements, which allows you to complete the device in accordance with the tasks and budget of the consumer.
• Illuminator. Very often, an ordinary mirror is used, which makes it possible to direct daylight onto the test sample. Currently, special halogen lamps are often used, which have a spectrum close to natural white light and do not cause gross color distortions.
• Diaphragm. Basically, microscopes use so-called "iris" diaphragms, so named because they contain petals similar to those of an iris flower. By shifting or expanding the petals, you can smoothly adjust the strength of the light flux that enters the sample that is not being studied.
• Collector. With the help of a collector located near the light source, a light flux is created that fills the condenser aperture.
• Condenser. This element, which is a converging lens, forms a light cone directed at the object. The intensity of illumination is controlled by the aperture. Most microscopes use a standard two-lens Abbe condenser.

It is worth noting that in an optical microscope one of two main methods of illumination can be used: illumination of transmitted light and illumination of reflected light. In the first case, the light flux passes through the object, as a result of which an image is formed. In the second - light is reflected from the surface of the object.

As for the optical system as a whole, depending on its structure, it is customary to distinguish direct microscopes (objectives, attachment, eyepieces are located above the object), inverted microscopes (the entire optical system is located under the object), stereoscopic microscopes (binocular microscopes, essentially consisting of two microscopes located at an angle to each other and forming a three-dimensional image).

Now let's move on to mechanical part of the microscope .

• tube. The tube is the tube that holds the eyepiece. The tube must be strong enough, it must not be deformed, which will worsen the optical properties, therefore only in the cheapest models the tube is made of plastic, but aluminum, stainless steel or special alloys are more often used. To eliminate "glare", the inside of the tube, as a rule, is covered with black light-absorbing paint.
• Base. Usually it is quite massive, made of metal casting, to ensure the stability of the microscope during operation. A tube holder, a tube, a condenser holder, focus knobs, a revolving device and a nozzle with eyepieces are attached to this base.
• Turret for quick lens changes. As a rule, in cheap models with only one lens, this element is absent. The presence of a revolving head allows you to quickly adjust the magnification, changing lenses by simply turning it.
• Subject table on which the test specimens are placed. These are either thin sections on glass slides - for "transmitted light" microscopes, or volumetric objects for "reflected light" microscopes.
• Mounts used to fix the slides on the slide table.
• Coarse focus screw. Allows, by changing the distance from the lens to the test sample, to achieve the clearest image.
• Fine focus screw. The same, only with a smaller pitch and less "travel" of the thread for the most accurate adjustment.

Special types of microscopy

Darkfield. A special condenser is used that highlights the contrasting structures of the unpainted material. Dark-field microscopy makes it possible to observe living objects. The observed object appears as illuminated in a dark field. In this case, the rays from the illuminator fall on the object from the side, and only scattered rays enter the microscope lenses.

Phase contrast microscopy allows you to study living and unpainted objects. When light passes through colored objects, the amplitude of the light wave changes, and when light passes through uncolored objects, the phase of the light wave changes, which is used to obtain a high-contrast image in phase-contrast and interference microscopy.

Polarizing microscopy - imaging of unstained anisotropic structures (eg collagen fibers and myofibrils).

interference microscopy combines the principles of phase-contrast and polarization microscopy and is used to obtain a contrast image of unstained objects.

Fluorescent microscopy used to observe fluorescent (luminescent) objects. In a fluorescent microscope, light from a powerful source passes through two filters. One filter traps light in front of the sample and allows light of the wavelength that excites the sample to fluoresce. The other filter allows light of the wavelength emitted by the fluorescent object to pass through. Thus, fluorescent objects absorb light of one wavelength and emit light in another region of the spectrum.

Fluorescent dyes (fluorescein, rhodamine, etc.) selectively bind to specific macromolecules.

electron microscopy

The theoretical resolution of the transmission EM is 0.002 nm. The real resolution of modern microscopes approaches 0.1 nm. For biological objects, the EM resolution in practice is 2 nm.

Translucent EM consists of a column through which electrons emitted by the cathode filament pass in vacuum. An electron beam focused by ring magnets passes through the prepared sample. The character of electron scattering depends on the density of the sample. Electrons passing through the sample are focused, observed on a fluorescent screen, and recorded using a photographic plate.

Scanning EM used to obtain a three-dimensional image of the surface of the object under study.

Chipping method ( freezing-cleavage) is used to study the internal structure of cell membranes. Cells are frozen at liquid nitrogen temperature in the presence of a cryoprotectant and used to make chips. The cleavage planes pass through the hydrophobic middle of the lipid bilayer. Nude inner surface membranes are shaded with platinum, the resulting replicas are studied in a scanning electron microscope.

2. The main parts of a light microscope, their purpose and device
The resolution of the microscope gives a separate image of two lines close to each other. The naked human eye has a resolution of about 1/10 mm or 100 microns. The best light microscope improves the capability of the human eye by about 500 times, i.e. its resolution is about 0.2 µm or 200 nm.

Resolution and magnification are not the same thing. If using a light microscope to take photographs of two lines located at a distance of less than 0.2 microns, then, no matter how you enlarge the image, the lines will merge into one. You can get a large magnification, but not improve its resolution.

Distinguish between useful and useless magnification. Useful is understood as such an increase in the observed object, in which it is possible to reveal new details of its structure. Useless is an increase in which, by increasing the object hundreds or more times, it is impossible to detect new details of the structure. For example, if an image obtained with a microscope (useful!) is enlarged many times more by projecting it onto a screen, then new, finer details of the structure will not be revealed, but only the sizes of existing structures will increase accordingly.

In educational laboratories, light microscopes are commonly used, on which micropreparations are examined using natural or artificial light. The most common light biological microscopes are: BIOLAM, MICMED, MBR (working biological microscope), MBI (biological research microscope) and MBS (biological stereoscopic microscope). They give an increase in the range from 56 to 1350 times. The stereo microscope (MBS) provides a truly three-dimensional perception of a micro-object and magnifies from 3.5 to 88 times.

In a microscope, two systems are distinguished: optical and mechanical. The optical system includes lenses, eyepieces and a lighting device (a condenser with a diaphragm and a light filter, a mirror or an electric illuminator).

The mechanical part of the microscope.

base (tripod) or massive leg (1);
box with micromechanism (2) and microscrew (3);

feed mechanism for rough aiming - a macro screw or rack (8);
object table (4);

screws (5, 6, 12, 13);

head (9); revolver (10); terminals; tube (11);

arc or tube holder (7);
Kremalera (macroscrew) - serves for an approximate "rough" installation on the photo

The mechanical system of the microscope consists of a stand, a box with a micrometer mechanism and a micrometer screw, a tube, a tube holder, a coarse aiming screw, a condenser bracket, a condenser displacement screw, a revolver, and an object stage.

Stand is the base of the microscope.

Box with micrometer mechanism m, built on the principle of interacting gears, is fixedly attached to the stand. The micrometer screw is used to slightly move the tube holder, and, consequently, the lens at distances measured in micrometers. A full turn of the micrometer screw moves the tube holder by 100 µm, and a turn by one division lowers or raises the tube holder by 2 µm. To avoid damage to the micrometer mechanism, it is allowed to turn the micrometer screw in one direction by no more than half a turn.

Tube or tube - cylinder into which eyepieces are inserted from above. The tube is movably connected to the head of the tube holder, it is fixed with a locking screw in a certain position. By loosening the locking screw, the tube can be removed.

Revolver designed for quick change of lenses that are screwed into its sockets. The centered position of the lens is provided by a latch located inside the revolver.

Screw coarse aiming is used to significantly move the tube holder, and, consequently, the lens in order to focus the object at low magnification.

The subject table is designed to place the drug on it. In the middle of the table there is a round hole into which the front lens of the condenser enters. On the table there are two springy terminals - clamps that secure the preparation.

Condenser bracket movably attached to the box of the micrometer mechanism. It can be raised or lowered by means of a screw that rotates a gear wheel, which is included in the grooves of the comb-cut rack.