The microscope device is its main parts. Microscope structure. Subtypes of light microscopes

The first concepts of a microscope are formed at school in biology lessons. There, children will learn in practice that with this optical device it is possible to view small objects that cannot be seen with the naked eye. The microscope and its structure are of interest to many schoolchildren. The continuation of these interesting lessons for some of them becomes 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.

Microscope structure

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

The stand holds on itself a tube with an eyepiece and a lens. A stage with an illuminator and a condenser is attached to the rack. An illuminator is a built-in lamp or mirror used 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 illumination, focusing beams 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 and 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 the light microscope is simple. These are the most affordable optical devices, they are the most widely used in practice. An eyepiece in the form of two magnifying glasses placed in a frame and a lens, which also consists of magnifying glasses tucked into the 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 also mounted a stage 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 an object of study placed on the stage by means of light rays passing through it with their further hitting the objective lens system. The same role is played by the eyepiece lenses, which are 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. A distinction is made between monocular, binocular or stereomicroscopes with one or two optical units.

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

Brightfield microscopy

The study of cells of microorganisms invisible to the naked eye, the size of which does not exceed tens and hundreds of micrometers (1 μm \u003d 0.001 mm), is possible only with the help of microscopes (from the Greek. mikros -small, skopeo -look). These devices allow one 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, carry out primary identification (from lat. idenificare- identification) of the studied organisms, they are observing 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).

Mechanical part of the microscope. This includes a tripod, a stage and a tube (tube).

Tripodhas a horseshoe-shaped base and an arc-shaped column (tube holder). It is adjoined by a box of mechanisms, a system of gear wheels for regulating the position of the tube. The system is driven by the rotation of the macrometric and micrometric screws.

Micrometer screw(rack, cog, macro screw) serves for preliminary orientation of the image of the object in question.

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

When the screws are rotated clockwise, the pipe is lowered towards the drug, when rotated counterclockwise, it rises from the drug.

The subject table is used to place the preparation with the object of study on it. The stage is rotated and moved in mutually perpendicular planes using screws. In the center of the table there is a round hole for illumination of the preparation from below with light beams directed by the microscope mirror. Two clips are mounted on the table (terminals)- springy metal plates designed to secure the drug.

If it is necessary to examine the surface of the preparation, avoiding gaps (which is important when counting), or if during work a re-examination of a specific area on the preparation is required, the stage will be interrupted drug provider.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 specimen guide, the center of rotation of the stage and the optical axis of the microscope system must be aligned with the centering plate of the specimen guide (hence the specimen stage with the specimen guide is sometimes called cruciform).

Tube (pipe) - the frame, which contains the elements of the optical system of the microscope. A revolver (lens 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 a main optical unit (lens and eyepiece) and an 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 device.

Lighting systemlocated under the stage. Mirrorreflects the incident light into the condenser . One side of the mirror is flat , the other - concave When working with the condenser, use only a flat mirror. A concave mirror is used when working without a capacitor with low magnification lenses. . Condenser(from lat . condenso- thicken, thicken), consisting of 2-3 short-focus lenses, collects the rays coming from the mirror , and directs 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 light intensity in the condenser there is iris(petal) diaphragm,made of steel crescent plates

Colored specimens are best viewed with an almost completely open diaphragm, unstained specimens with a reduced diaphragm opening .

Located under the condenser ring-shaped holderfor light filters (usually blue and white are attached to the microscope frosted glass). When working with an artificial light source, the filters give the impression of daylight , which makes microscopy less tiring on the eyes.

Lens(from lat. objectum- object) is the most important part of the microscope. This is a multi-lens short-focus system, on the quality of which the image of the object mainly depends. The outer lens facing the flat side of the drug is called the frontal lens. It is she who provides an increase . The rest of the lenses in the objective system mainly perform the functions of correcting optical defects that arise when examining objects. .

One such disadvantage is the phenomenon spherical aberration.It is associated with the property of lenses to unevenly refract peripheral and central beams. The former tend to be more refracted than the latter, and therefore intersect at a closer distance to the lens, resulting in the image of the dot acquiring the appearance of a blurred spot.

Chromatic aberrationarises when a beam of rays with different wavelengths passes through the lens . Refracting in different ways , rays do not intersect at one point. Shorter wavelength blue-violet rays are refracted more than longer wavelength red rays. 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 elusive. Best material for achromat lenses - flint glasses - old types of glass with a high content of lead oxide.

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

Planachromats -a kind of apochromats with a flat field of view. Objectives-planachromats completely eliminate the curvature of the field of view, which causes uneven focusing of the object (with curvature of the field of view, only part of the field is focused). Planachromats and planapochromats are used for microphotography.

Lenses are dry and submersible (immersion). At work with dryobjectives between the frontal objective lens and the object of study is air. Optical calculation immersionlenses provide for their operation when the frontal 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 are deflected and do not enter the observer's eye (Fig. 1).

When working with an immersion lens, place between the cover slip and the objective lens cedar

butter,the refractive index of which is close to the refractive index of glass (Table 1).

The rays in an optically homogeneous homogeneous medium do not change their direction. Immersion lenses on the frame have black circular cutting 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- the 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- lens focal length: the larger it is, the lower the lens magnification.

The magnification of the lenses is indicated on their mounts (8x, 40x, 9x). Each lens is also characterized by a specific working distance in millimeters.

Low magnification lenses have a greater distance from the frontal objective lens to the specimen than high magnification lenses. So, lenses with a magnification of 8 x, 40 x and 90 x, respectively, have a working distance of 13.8; 0.6 and 0.12 mm. Depending on which lens you are working with, a macro and micrometric screw is selected to focus it. An immersion lens has a working distance of 0.12mm to the lens, so it is often called “myopic”.

1 Cedar nut oil is obtained from the seeds of the Virginia juniper Juniperus virginianaor Zeravshan juniper Juniperus seravschana.Currently, synthetic products are more often used as an immersion liquid, which correspond to the optical properties of cedar oil.

A microscope (from the Greek mikros - small and skopeo - I look at) is an optical device 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 adaptations, but are similar to each other in their basic elements.

Figure: 33. Microscope device

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

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

The microscope consists of two main parts: mechanicaland optical(fig. 33). The mechanical part of the microscope includes a stand (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 like " 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 a stage (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 in 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 microscopes 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 ratchet) and small handles (6) or a disk for fine focusing of the microscope (micrometric screw). Rotating the rack, produce rough, visible to the eye, vertical movement of the stage or tube. With the help of a micrometer screw, the stage or tube is moved up and down a very small distance, visible only during microscopy. One turn of the micrometer screw gives a movement of 0.1 mm. This is sufficient to accurately focus the subject. To avoid breakage of the micrometer screw, do not make it more than 1-1.5 revolutions.

Optical partthe microscope includes an illumination system and a lens system.

Lightingthe system is located under the stage and consists of a condenser (7) and a lighting device (8). The condenser is an essential part of the microscope on which the success of microbiological research depends. It is designed to collect scattered light rays, which, passing through the lens of the condenser, are collected in focus on the plane of the specimen under consideration.

The condenser is secured with a ring in a rim located on a bracket and held in place 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 with a special lever, which makes it possible to change the brightness of the object illumination. At the bottom of the condenser there is a movable frame (frame), into which light filters made of frosted or blue glass are placed. Light filters are used to reduce the amount of light 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 systemlens, which creates a magnified reverse and ghost image of an 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.

Lensis a metal cylinder in which the lenses are fixed. The main (frontal) lens is directed towards the specimen. Only it provides the necessary magnification of the displayed object, all the rest correct the image and are called correctional. The resolution of the microscope depends on the front lens, i.e. the smallest distance at which two closely spaced points are distinguished separately. In modern optical microscopes, the resolution of objectives is 0.2 microns. The more the curvature of the frontal lens, the more degree its increase.

However, the frontal lens also causes negative, interfering with research, phenomena, the main of which are spherical aberration and chromatic aberration.

Spherical aberration is associated with the fact that the side rays incident on the edges of the frontal lens are refracted more strongly than the others and make the image of the object blurry, indistinct. Therefore, each point of the object looks like a circle. To correct the shortcomings of the front lens in objectives - 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 the frontal lens into its component parts of the spectrum. The image of the object appears as if surrounded by a rainbow. Glass lenses most strongly refract blue-violet rays and least of all - red ones.

Elimination of spherical and chromatic aberration is most fully achieved when using apochromats. They consist of a set of lenses with 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 reproduction of the color of colored objects.

At first, they used achromats,which made it possible to eliminate chromatic aberration in relation to the two brightest colors of the spectrum. Therefore, the image of the object was devoid of color. Later, special types of glass were obtained, the lenses from 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.

Panachromatshave 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 bodies: achr. - achromat, apo. - apochromat; pan. - panchromat

Distinguish between dry and immersion lenses. 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 glass of the preparation, then again through air gap, as a result of which they are refracted and scattered at the boundary of dissimilar media. After such transitions through dissimilar media, only a part of the light rays penetrates the lens. To capture the maximum amount of light rays, the front lens of objectives must have a relatively large diameter, large focal length, and small curvature. Therefore, dry lenses have a low magnification ratio (8 x, 10 x, 20 x, 40 x).

To achieve higher magnification, it is necessary to create a homogeneous optical medium between the frontal objective lens and the preparation. This becomes possible when the lens is immersed in a drop of cedarwood oil, which is applied to the preparation. Cedar oil has a refractive index n \u003d 1.515, which is close to the refractive index of the glass of the preparation (n \u003d 1.52). Therefore, light rays passing through the immersion oil do not scatter and, without changing their direction, enter the lens, providing a clear visibility of the object under study. In the absence of cedar nut oil, substitutes are used: peach oil (n \u003d 1.49); castor oil (1.48-1.49); clove oil (1.53); immersiol, which contains peach oil (50 g), rosin (10 g), naphthalene (10 g), salol (1 g); a mixture of equal volumes of castor (n \u003d 1.47) and dill (n - 1.52) oils.

Oil immersion lenses are marked with "MI", a black stripe on the cylinder and a sunken front lens, which protects it from damage in case of careless contact of the lens with the drug. The magnification of an oil immersion lens can be 80 x, 90 x, 95 x, 100 x and 120 x.

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

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

Eyepiecelocated at the top of the barrel and magnifies the image given by the lens. It consists of two flat-curved lenses: the upper lens (ocular) and the lower lens, which is facing the object, collecting the lens. The eye of the researcher, 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 barrel of the eyepieces indicating how many times the eyepiece increases the magnification of the objective. A monocular microscope uses one objective, while a binocular microscope uses two. Accordingly, the image of the object is obtained flat or stereoscopic. The binocular tube can be adjusted to any interpupillary distance between 55 and 75 cm.

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

However, the magnified image of an object may be clear or unclear. The clarity of the image is determined by the resolution of the microscope (useful magnification) i.e. the minimum distance between two points when they have not yet merged into one. The higher the resolution of the microscope, the smaller the object can be seen.

The resolution index of the microscope depends on the wavelength of the light used and the sum of the numerical apertures of the objective and condenser:

where α is the minimum distance between two points;

And 1 - numerical aperture of the objective;

And 2 - numerical aperture of the condenser;

λ is the wavelength of the light used.

The numerical apertures of the lens and condenser are indicated on their housing. You can increase the resolution of the microscope using ultraviolet radiation. However, ultraviolet microscopes are very expensive, making them difficult to use. Most often, an immersion system is used to increase the resolution of the microscope.

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The design of a 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 one. This article will detail the structure optical light microscope, which is currently the most popular choice for amateurs and professionals, and with which you can solve many research problems.

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

Optical and mechanical parts can be distinguished in the microscope. The microscope optics includes objectives, eyepieces, and an illumination system. A tripod, tube, stage, condenser and light filter mounts, mechanisms for adjusting the stage and tube holder constitute the mechanical part of the microscope.

Let's start with optical part .

• Eyepiece... That part of the optical system that is directly connected with the eyes of the observer. In the simplest case, a lens consists of one lens. Sometimes for more 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... Probably 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 section "Main parameters of microscopes". Objectives are divided into "dry" and "immersion", achromatic and apochromatic, and even in cheap simple microscopes represent a rather complex system of lenses. Some microscopes have unified lens mounts, which allows the device to be completed in accordance with the tasks and budget of the consumer.
• Illuminator... A common mirror is often used to direct daylight onto the sample under study. At present, special halogen lamps are often used, which have a spectrum close to natural white light and do not cause gross color distortions.
• Diaphragm... Mostly microscopes use so-called "iris" diaphragms, so named because they contain petals similar to those of an iris flower. By moving or moving apart the petals, you can smoothly regulate the strength of the light flux entering the sample not under investigation.
• Collector... A collector located near the light source creates a luminous flux that fills the aperture of the condenser.
• Condenser... This element, which is a collecting lens, forms a cone of light directed towards the object. The light intensity is controlled by the diaphragm. Most commonly, microscopes use a standard two-lens Abbe condenser.

It is worth notingthat in an optical microscope one of two main illumination methods 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, the 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 straight microscopes (objectives, attachments, eyepieces are located above the object), inverted microscopes (the entire optical system is located under the object), stereoscopic microscopes (binocular microscopes, consisting essentially of two microscopes located at an angle to each other and forming a volumetric image).

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

• Tube... The tube is the tube that houses the eyepiece. The tube should be strong enough, should not deform, which will worsen the optical properties, because only in the cheapest models the tube is made of plastic, more often aluminum, stainless steel or special alloys are used. To eliminate glare, the tube inside is usually covered with black light-absorbing paint.
• Base... Usually it is made of a massive enough metal casting to ensure stability of the microscope during operation. On this base, a tube holder, a tube, a condenser holder, focusing knobs, a revolving device and an eyepiece attachment are attached.
• Turret for quick lens change. 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 objectives by simply turning it.
• Subject table, on which the test samples are placed. These are either thin sections on glass slides for "transmitted light" microscopes, or volumetric objects for "reflected light" microscopes.
• Mountingswith which the slides are fixed on the stage.
• Coarse focus adjustment screw... Allows, by changing the distance from the objective to the test sample, to achieve the clearest image.
• Fine focus screw... The same, only with a smaller pitch and a smaller "stroke" of the thread for the most precise adjustment.

Special types of microscopy

Darkfield. A special condenser is used to highlight the contrasting structures of the unpainted material. Dark-field microscopy allows you to observe living objects. The observed object looks like it is lit 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 live 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 - the formation of an image of unstained anisotropic structures (for example, collagen fibers and myofibrils).

Interference microscopy combines the principles of phase contrast and polarization microscopy and is used to obtain a contrast image of uncolored objects.

Luminescence microscopy used to observe fluorescent (luminescent) objects. In a fluorescent microscope, light from a powerful source passes through two filters. One filter blocks light in front of the sample and transmits light at a wavelength that excites fluorescence in the sample. Another filter transmits light of the wavelength emitted by the fluorescent object. Thus, fluorescent objects absorb light at one wavelength and emit at 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 is approaching 0.1 nm. For biological objects, EM resolution in practice is 2 nm.

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

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

Chipping method ( freezing-cleaving) is used to study the internal structure of cell membranes. The cells are frozen at liquid nitrogen temperature in the presence of a cryoprotectant and used for making chips. Cleavage planes pass through the hydrophobic middle of the lipid bilayer. The exposed inner surface of the membranes is shaded with platinum, and the resulting replicas are examined under a scanning electron microscope.

2.The main parts of the light microscope, their purpose and design
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, photographs of two lines located at a distance of less than 0.2 microns are obtained, then, as if not to 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 magnifications. Useful means such an increase in the observed object, at which new details of its structure can be revealed. Useless is an increase in which, by enlarging an object hundreds or more times, it is impossible to find new structural details. For example, if an image obtained with a microscope (useful!) Is enlarged many times 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 teaching laboratories, light microscopes are usually used, on which slides are examined using natural or artificial light. The most common biological light microscopes are: BIOLAM, MIKMED, MBR (biological working microscope), MBI (biological research microscope) and MBS (biological stereoscopic microscope). They give an increase in the range from 56 to 1350 times. A stereomicroscope (MBS) provides a truly volumetric 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 objectives, eyepieces and an illumination device (a condenser with a diaphragm and a light filter, a mirror or an electric light).

Mechanical part of the microscope.

base (tripod) or massive leg (1);
a box with a micro-mechanism (2) and a micro-screw (3);

feed mechanism for coarse aiming - macroscrew or ratchet (8);
subject table (4);

screws (5, 6, 12, 13);

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

arc or tube holder (7);
Cremaliera (macro screw) - serves for an approximate "rough" installation on the background

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 moving screw, a revolver, and a stage.

Stand is the base of the microscope.

Micrometer boxm, built on the principle of interacting gears, is fixed to the stand. The micrometer screw is used for a slight movement of the tube holder, and, consequently, the lens at distances measured by micrometers. A full turn of the micrometer screw moves the tube holder by 100 microns, and a turn by one division lowers or raises the tube holder by 2 microns. To avoid damage to the micrometer mechanism, it is allowed to turn the micrometer screw in one direction no more than half a turn.

Tube or tube - cylinder, into which the 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.

Revolverdesigned 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 intended for placing the drug on it. There is a round hole in the middle of the stage, into which the front lens of the condenser fits. There are two springy clips on the table - clips that secure the drug.

Condenser bracket movably attached to the micrometer mechanism box. It can be raised or lowered by means of a screw that rotates a gearwheel that fits into the grooves of the comb rack.