metallurgical microscope

Metallographic microscope, also known as reflective polarizing microscope or mineral microscope, is a basic tool for mineralogical research. In recent decades, the development of mineral microscope has made a lot of progress, and its optical performance has been greatly improved. So that mineralogists can accurately observe more optical characteristics. At the same time, several optical instruments and microscope accessories designed to quantitatively test the physical and optical properties of opaque minerals have also been widely used, thus creating favorable conditions for mineralogical research.

The mineral microscope is actually composed of a polarizing microscope and a set of "vertical illumination system" (Figure 1- 1). Most of the "vertical illuminators" of the old mineral microscope are fixed at the lower end of the lens barrel, while the new ones can be disassembled at will. After installing the vertical illuminator, it can be used to observe the reflected light. When the "vertical illuminator" is removed, it can be used for observation under transmitted light by installing an objective lens converter and an objective lens for light transmission observation.

I. Structure and Accessories of Metallographic Microscope

The mirror body of mineral microscope is basically the same as that of general polarizing microscope (rock microscope). The main components of mineral microscope are briefly introduced below.

(1) vertical illuminator

The vertical illuminator with light source constitutes a complete vertical illumination system. The system and components are as follows (Figure 1- 1).

Figure 1- 1 Schematic diagram of vertical lighting assembly and system light path of mineral microscope.

Vertical lighting assembly:1-light source; 2- condenser lens; 3— Aperture diaphragm; 4- field of view diaphragm; 5- polarizer; 6 field lens (correction lens); 7- reflector; 8— Lens system of objective lens; 3 '- image of aperture stop; 4 '- image of the field stop; 9- optical film

1. aperture stop

Aperture diaphragm, also known as aperture diaphragm, is an iris diaphragm that can be opened and closed at will behind the lens of light source. It is used to control the diameter of the incident beam, the contrast of the image and the effective aperture of the objective lens. When it is reduced, the diameter of the incident beam is also reduced, so the brightness of the viewing area is also weakened, but relatively vertical incident light can be formed, thus reducing harmful clutter light, improving image contrast and making it clear. However, the effective aperture of the objective lens is reduced, so that the resolution will be reduced. Therefore, it is necessary to properly adjust the aperture stop, and the adjustment method is described in detail below.

2. Polarizer

Polarizer, also known as front polarizer, is made of polarizer, and its function is to polarize incident light on a straight line (plane). Should be free to rotate at least 90, preferably locked. When observing the ore light curtain, the vibration direction should be east-west (horizontal vibration), because the light intensity reflected downward by the reflector is greater than that in the north-south position. However, the front polarizer of the new microscope is mostly fixed in the east-west direction.

3. Field of view diaphragm

Visual field diaphragm, also known as visual field diaphragm, is generally an iris diaphragm composed of movable blades. Its function is to control the size of the field of view (field) and prevent harmful and disorderly reflected light from entering the field of view, so as to improve the clarity of the observed mineral image and facilitate detailed research on it. In general observation, this aperture can be adjusted to coincide with the edge of the field of vision and should not be too large to avoid more messy light being thrown into the field of vision.

Located behind the field stop, a field lens (also called correction lens or achromatic lens) consisting of two or three lenses is usually installed. It can move back and forth, but it is also fixed. Its function is to make the focus of the visual field diaphragm accurate, so as to make the image in the visual field clear.

4. Reflector

The reflector is the most important part in the vertical illuminator, and its function is to reflect the horizontal incident light vertically downward. The most commonly used mirrors are glass and prism, and the other is a new Smith mirror. The following will introduce three kinds of reflectors:

Fig. 1-2 glass mirror (a) and prism mirror (b) and their reflection principles.

1- light bulb; 2- condenser lens; 3— Aperture diaphragm; 4- polarizer; 5- field of view diaphragm; 6-field lens; 7- reflector; 8- objective lens; 9— Free working distance; 10-optical film

(1) glass plate reflector This reflector is made by installing a glass plate with an inclination of 45 in a vertical illuminator (Figure 1-2a). The reflective surface of glass plate is usually coated with a transparent film of high refractive index substances (such as zinc sulfide or bismuth oxide) to improve its reflective ability. At the same time, in order to enhance the upward transmission ability of light through it, the upper surface of the glass plate is coated with an antireflection film of low refractive index substances (such as magnesium fluoride). As can be seen from figure 1-2a, the incident light is incident on the reflective glass sheet, part of it is lost through the glass sheet, and the other part is reflected downward to the surface of the miner's lamp through the objective lens. When the miner's lamp surface reflects upwards and meets the glass sheet again, part of the light is reflected and turned to the light source, and the other part is lost to the eyepiece through the glass sheet. The illumination light is incident from the light source and reflected twice by the glass sheet, and the maximum light intensity reaching the eyepiece is 2 1% ~ 22% of the incident light intensity (let the reflectivity of the light sheet be 100%). It can be seen that the main disadvantages of glass mirror are weak reflection ability, that is, large loss of incident light and low brightness of field of view. The advantage of the glass reflector is that the light can pass through the full aperture of the objective lens, so the resolution is strong and the brightness in the field of view is uniform, so it must be used when observing the polarization diagram, and because more vertical light can be obtained, it should also be used when measuring the reflectivity. In addition, it can also be used to take photos with uniform brightness in microphotography.

(2) Prism reflector Total reflection Prism reflector uses right-angle prism instead of glass sheet (Figure 1-2b). The incident light is totally reflected downward by the prism, but because the size of the prism is not more than half of the inner diameter of the lens barrel, half of the space must be reserved as the upward path of the reflected light, so the maximum light intensity reaching the eyepiece is not more than 50%, so the brightness of the field of view is much higher than that when the glass reflector is used. There are two kinds of prism reflectors. Old-fashioned microscopes mostly use ordinary right-angle prisms. Its main disadvantage is that when the incident light is linearly polarized, because the light beams are not completely parallel (oblique light), some reflected light will be elliptically polarized after being reflected by the prism, thus affecting the accurate observation of optical properties.

All new mineral microscopes adopt cubic total reflection compensation prism (Figure 1-3). The refractive index of prism glass with triple total reflection must be such that the phase difference caused by the first total reflection is 60, and the total phase difference after the third total reflection should be 180, which is still linear polarization.

Figure 1-3 Triple Total Reflection Compensation Prism

Figure 1-4 Smith reflector

In a word, the prism mirror has less light loss than the glass sheet, so the field of view is brighter. At the same time, there is less harmful clutter reflected light. Because the incident light is slightly inclined on the mineral optical sheet, the contrast in the field of vision is sharp and the image is clear. However, because the light it emits to the eyepiece is not uniform enough, the field of vision is slightly half bright and half dark (this defect is not obvious if the medium and low power objective lens is used). Because the prism blocks half of the aperture of the objective lens and can only see half of the polarization diagram, it is not suitable for observing the polarization diagram.

(3) Smith reflector Smith reflector is a kind of secondary reflection structure, which consists of a mirror and a reflective glass sheet. Its structure is shown in figure 1-4. The incident light is reflected by the mirror M onto the coated glass sheet G, then reflected by the glass sheet G, and vertically downwards enters the objective lens onto the optical sheet S. The incident angle α of the light from the light source to the mirror M is 22.5, and the incident angle of the mirror to the glass sheet is also 22.5. The reflector is made of aluminized glass sheet with refractive index of 1.52. The lower surface of the reflector is coated with bismuth oxide (Bi2O3) film with n = 2.45 to enhance reflectivity, and the upper surface is coated with magnesium fluoride (MgF2) film with n = 1.38 to reduce internal reflection and enhance transmittance.

This kind of reflector not only has the advantages of glass plate reflector, but also can greatly reduce the reflection and transmission rotation of glass plate because there is little difference between the transmitted and reflected light intensity of polarized light on the vertical incident plane and the parallel incident plane.

(2) Lighting equipment

1. light source

The light source of mineral microscope generally adopts tungsten filament incandescent lamp and tungsten halogen lamp. Some research microscopes are also equipped with mercury lamps, sodium lamps, indium lamps or xenon lamps.

2. Optical filter

In addition to the necessary blue glass filter, the above light source also needs a monochromatic light source for some special purposes (such as measuring the reflectivity of minerals and the heterogeneous apparent rotation angle Ar). ). Monochrome light source mainly includes monochromator and interference filter. Except monochromators, most of them use simple and convenient interference filters. Ordinary glass filters have been basically eliminated because of their poor monochromaticity and complex spectral components. However, interference filters are widely used because of their narrow wavelength range (narrow half width) and high monochromaticity.

The interference filter is composed of two parallel optical glass sheets, the inner surface of which has a translucent silver or aluminum film, and a transparent dielectric with a thickness of about half the specified transmission wavelength is sandwiched between the glass sheets. The incident light is repeatedly reflected between the two inner surfaces, and monochromatic light is emitted from the glass after interference. Its performance depends on three constants: ① the peak position of transmitted light; ② Peak transmittance and transmission band transmittance; ③ The half-width HW of the transmission band, that is, the transmission width at the half-peak height, can be controlled around 10 nm, and filters with various wavelengths and different half-widths can be calculated and designed. The interference filter has good monochromaticity, large aperture and sufficient light input.

According to the regulations of Mineralogy Committee (COM) of the International Association of Minerals, the reflectivity of each mineral should be measured at least at 470nm, 546nm, 589nm and 650nm, so these four-wavelength filters are necessary.

(3) Connect the objective lens

The objective lens, commonly known as the objective lens, is an optical amplification system composed of many lenses with different shapes. Each objective lens has two basic characteristics, namely, magnification and resolution. According to magnification, the objective lens can be divided into low magnification (magnification several times, that is, less than ten times), medium magnification (magnification about ten to twenty times) and high magnification (magnification more than twenty times).

1. Resolution of the objective lens

Resolution refers to the ability to distinguish the fine structure, that is, the ability to display the fine structure characteristics of the observed object. It is often expressed as resolution L, which means the shortest distance that the objective lens can separate two points (or two parallel lines). For example, when observed with an objective lens, two points with a distance of 0.4 micron can be separated, and two points with a distance of 0.3 micron cannot be separated, so 0.4 micron is the resolution (resolution limit) of this objective lens.

The resolution of the objective lens is not only related to various aberrations of the objective lens, but also depends on its "numerical aperture NA". And na = nsin α, α is the cone angle between the front lens of the objective lens and the focal point on the optical sheet, that is, half the aperture angle (Figure 1-5).

Figure 1-5 aperture angle (aperture angle) of objective lens

mineralography

Where: n is the refractive index of the observation medium between the objective lens and the optical sheet; λ is the wavelength of light wave used for observation.

As can be seen from the above formula, the larger the numerical aperture NA of the objective lens, the smaller the resolution, that is, the stronger the ability to distinguish fine structures; The shorter the wavelength of the incident light wave, the smaller the resolution L. Therefore, in order to enhance the resolution of the objective lens (make L smaller), it is mainly necessary to increase the numerical aperture NA. In fact, the maximum aperture angle of high power objective lens is 144, that is, ∠ α is 72, so the maximum numerical aperture in air medium is na = 1× sin72 = 0.95. When oil immersion (fragrant asphalt n = 1.5 15) is used as the medium, na =1.515× sin67 =1.40. Therefore, the maximum numerical aperture does not exceed 1.40. The numerical aperture (0.05 ~ 1.4) is generally engraved on the objective lens. If you want to observe subtle phenomena, you can choose an oil-immersed objective with a high numerical aperture. It must be pointed out that there is still glare at the lens interface in the objective lens for reflection, which also affects the resolution, so the resolution of the objective lens cannot be based only on the numerical aperture.

It should also be pointed out that the resolution and magnification must be separated, and they are not completely proportional, that is, the larger the object, the clearer the fine structure. Because if you don't increase the resolution and only increase the magnification, the image will be blurred, so it is useless "empty magnification". Therefore, the performance of the microscope mainly depends on the resolution or resolution, rather than the simple amplification ability.

The objective lens is generally engraved with magnification and numerical aperture. The magnification is sometimes indicated by the symbol "×", such as10x or10x. Usually, the "×" sign is omitted and only the number is engraved; There is also a focal length f or mm without engraving amplification. For example, f 5.2 means that the focal length is 5.2 mm. The numerical aperture is usually represented by "NA", but the numbers are usually directly engraved on the objective lens housing, such as "10/0.20" with magnification of10, and the numerical aperture is 0.20.

2. Aberration of lens and its correction

Enlarged images of Dan Toujing are usually distorted or colored. This phenomenon is caused by various aberrations of the lens. When any lens or a group of lenses are imaging, due to the defects of the optical conditions of the lens itself, various abnormalities will appear in the object image. These abnormal effects are collectively called aberrations.

Aberrations include spherical aberration, longitudinal chromatic aberration, transverse chromatic aberration, comet aberration, astigmatism, image field bending and distortion. However, the first two aberrations are more prominent.

(1) spherical aberration spherical aberration is called spherical aberration for short. As can be seen from Figure 1-6, the parallel beams from infinity pass through the convex lens and are not focused at one point (i.e. the focal point of the lens), but at multiple points. As shown in the figure, three pairs of light converge into three focal points, and the closer to the optical axis, the smaller the light refraction, so the farther the focal point is from the lens; The closer the lens edge is, the stronger the refraction of light is, so the closer the focus is to the lens. Because the reason for this phenomenon is that the lens surface is spherical, it is called spherical aberration. Because of this aberration, when the central part is clearly imaged by lifting the lens barrel, the edge part is not clear, and if the edge is clear, the central part is blurred. The correction method is to combine the positive (convex) negative (concave) lens with optical glass with different refractive indexes through calculation, so that the spherical aberration formed by the two lenses is opposite and offset, thus correcting the spherical aberration of the lens. But the overall correction is not complete, and there are still some ball errors.

Figure 1-6 spherical aberration

P screen

(2) Color difference Color difference is also called color difference. Because glass has different refractive indexes for colored light with different wavelengths, white light cannot be focused on one point after passing through the lens, that is, chromatic aberration occurs. There are two kinds of color difference, vertical and horizontal, the former has great influence, and the generation of longitudinal color difference is shown in figure 1-7. After the white light emitted by the point object passes through the lens, the blue light has the strongest refraction, focusing on A, green light on B and red light on C, so the image of the object is inevitably unclear.

Figure 1-7 Longitudinal chromatic aberration

A- blue light focusing; B- green focus; C- red focus

Vertical chromatic aberration will cause rainbow-like color edges in the object image, so it must be corrected. Generally, spherical aberration is corrected at the same time, that is, glass with different refractive index and average dispersion coefficient is made into positive and negative lenses after calculation, so that most spherical aberration and longitudinal chromatic aberration can be corrected at the same time. The objective lens made of this combination is called achromatic objective lens and apochromatic objective lens.

3. Type and identification of objective lens

Objective lenses are classified according to numerical aperture and magnification, and there are many different uses. At present, only the performance and use of the objective lens of mineral microscope are briefly introduced as follows:

(1) can be divided into dry (air, dry) objective lens and immersion (oil, water) objective lens according to the different observation media used. The observation medium of the drying objective lens is air; The most commonly used immersion objective is oil-immersed objective, and the medium is aromatic asphalt (n = 1.5 15) which is not easy to corrode the lens. Its logo is a colored circle (usually black) at the front end of the metal frame of the objective lens, and it is engraved with "oil", "Oel", "imm" or "пми". Because the numerical aperture NA of the oil-immersed objective lens is larger than that of the dry objective lens and has strong resolution, it is easy to observe the optical properties of minerals such as double reflection, inhomogeneity and internal reflection.

(2) According to the degree of aberration correction, the objective lens can be divided into achromatic objective lens, apochromatic objective lens, semi-apochromatic objective lens and flat objective lens. Achromatic objective focuses red and blue light in visible light at one point, while yellow-green light focuses at another point (near the focus of red and blue light). Therefore, the chromatic aberration and spherical aberration of the above-mentioned colored light are basically corrected, but the chromatic aberration of various colored lights except red and blue light is not corrected, and achromatic objective lenses generally do not engrave symbols.

Apochromatic objective lens can basically focus the light of various colors in the visible spectrum on one point, and can also correct spherical aberration and other aberrations. This kind of objective lens has good performance and is suitable for observation and photography of various multiples. But its structure is complex, and it is made of special optical glass or fluorite with optical glass. Its objective lens shell is engraved with the words "APO" or "apochromatic". The structure of the semi-apochromatic objective lens is the same as that of the achromatic objective lens, except that the crown glass is partially or completely replaced by optical fluorite. Its chromatic aberration correction is between achromatic and apochromatic. The object frame is engraved with the words "F 1", "Neofluar" or "fluent".

All the above objective lenses have image field curvature, and the higher the multiple, the more serious it is, especially the apochromatic objective lens. Most new microscopes use a flat objective. The characteristic of flat objective lens is that the image they form is basically flat and the image field is very small, so there will be no phenomenon that the center and edge of the field of view cannot be focused at the same time, which is beneficial to observation and micrography. Its identification mark is engraved with the words "Plan Chromate", "Plan Chromate", "Plan", "pl", "Npl" and "Epiplan" on its metal frame.

Finally, it must be mentioned that the mineral microscope cannot use the deformable objective lens, which is especially not suitable for observing minerals under orthogonal polarization. The strain-free objective lens is marked with the words "POL" or "p"; "(p)" means basically no strain. It should also be pointed out that there are two groups of objective lenses (reflected light and transmitted light) in polarization and reflection microscope, and each group has a label, so it is not allowed to mix them, especially high-power objective lenses.

(4) glasses

The objective lens magnifies a tiny object, but because the object is too small, the real image is still not big enough, so it is necessary to add a magnifying glass between the real image and the eyes to further enlarge the real image and turn it into an enlarged virtual image for easy observation. This magnifying glass is the eyepiece, also called the eyepiece. According to their different structures and uses, they can be divided into the following categories.

1. Huygens eyepiece

It consists of two plano-convex lenses (figure 1-8a), the convex surface faces downwards, and the eyepiece at the upper end is smaller than the field lens at the lower end. The focus of the eyepiece is between the two lenses (the focal plane is equipped with a metal frame for placing eyepiece micrometer or crosshair), so it is called negative eyepiece. The advantage of Huygens eyepiece is that it can completely eliminate its lateral chromatic aberration. Its magnification is very small, the maximum is not more than 10 times. This kind of eyepiece has been gradually replaced by flat-image eyepiece because it can not correct spherical aberration and longitudinal chromatic aberration well, and it is inconvenient for human eyes to stick to the eyepiece when observing.

Figure 1-8 shows two common types of eyepieces.

2. Ramston eyepiece

It also consists of two plano-convex lenses with opposite convex surfaces (Figure 1-8b). The focus of the eyepiece is under the objective lens, so it is also called the positive eyepiece. It is suitable to install a micrometer on its focal plane, because the micrometer and the object image are magnified by two lenses, so there is basically no aberration. However, this kind of eyepiece can not completely eliminate the lateral chromatic aberration. The improvement is to stick the eye lens together with two lenses to eliminate the residual chromatic aberration, so it is called Chelner eyepiece, that is, undistorted eyepiece. Chelner eyepiece is engraved with "O", "Orth" and "Opt" on the shell. Due to the design of planar image compensation eyepiece in recent years, the eyepiece is not used in the new microscope except that it can be attached to the old microscope.

3. Compensating eyepiece

This is an eyepiece specially used for apochromatic objective lens. Because the blue image formed by the apochromatic objective lens is larger than the red image, and the red image designed by the compensation eyepiece is larger than the blue image, the lateral chromatic aberration of the apochromatic objective lens is offset. The compensation eyepiece can also be used in conjunction with fluorite objective and high-power achromatic objective. However, the general achromatic objective lens with compensation eyepiece will make the object image have colored edges. In addition, the biggest disadvantage of this eyepiece is that the image field is seriously bent.

The magnification of the compensation eyepiece varies from 5 times to 30 times. Its shell is often engraved with words such as "C", "K" and "Compens".

At present, the new polarizing microscope or mineral microscope only uses flat eyepiece, which has been eliminated.

4. Flat-image eyepiece

It is also a kind of compensation eyepiece, but it eliminates the image field bending. This kind of eyepiece only corrects its own image field curvature, but can't correct the image field curvature of the objective lens. Only when it is combined with a flat objective lens can a completely flat image field be obtained. The magnification of the flat eyepiece is from 8 times to 25 times; The words "Plan", "Planosc-opic", "Periplan", "Kpl", "GW" or "GF" are usually engraved on the shell.

Two. Brief introduction of several common metallographic microscopes

Metallographic microscope is the most basic and important instrument in mineralogical research. Therefore, we must learn to use it skillfully and fully grasp the name and performance of each of its accessories. Now briefly introduce two common microscopes as follows (Figure 1-9).

1. Olympus bx5 1m (bx60m) reflective microscope

This is the latest mineral microscope made in Japan. The vertical illuminator is connected with the mirror body and equipped with a front polarizer and an upper polarizer. The upper polarizer can rotate once, and the scale is marked 180. The vibration direction of the upper polarizer can be changed 180. The transformer is mounted in the frame and the knob is on the right hand, which is very convenient. In addition, when adjusting the light intensity, there are 12 indicator lights on the frame. The frame is Y-shaped, which makes the microscope stable. The microscope has large field of view, no distortion, clear object image, light intensity under orthogonal polarization, and is suitable for observing internal reflection and polarization color, uniformity and non-uniformity. The measurement accuracy of ar angle is 0.65438 0.

Figure 1-9 metallographic microscope

2. Ortholux Ⅱ POL-BK microscope

Microscope is also a dual-purpose mirror, which is a product of Lai Ci factory. It is also equipped with an upper polarizer, a lower polarizer and a front polarizer. The upper polarizer can rotate 360, and the scale value is accurate to 0. 1. The vertical illuminator is connected with the mirror body; There is a glass sheet and a prism reflector, which can be selected. The lighting lamp is a lamp room that can be disassembled from the mirror body, and there are 12 V and 50 W ~ 100 W tungsten bromide lamps in it. The microscope has good performance and can be used to measure some optical constants.

3.LABORLUX 12 polarizing microscope

This is also a dual-purpose microscope, which is a new product improved by Lai Ci factory. The basic components in the vertical lighting lamp are complete and connected with the mirror body and the lighting lamp; The lighting lamp is a lamp room that can be disassembled from the mirror body, and there are 6 V and 20 W bromine tungsten lamps in it. The transformer is placed in the mirror body, which is convenient to adjust the illumination brightness. This microscope has good performance and is suitable for experimental work and students.

III. Adjustment, Use and Maintenance of Mineral Microscope

1. Adjustment of metallographic microscope

No matter what the performance of the microscope is, it must be adjusted before use, so that all its components are in the correct position, and effective observation can be carried out. The structure of mineral microscope is complex, and many parts need to be carefully checked and adjusted during installation and use. The parts that usually need to be adjusted are briefly described as follows:

(1) Adjusting the light source At present, most of the lamps of new microscopes are installed on the mirror body, such as in the front end of a vertical illuminator or in a lamp room. The adjustment method is to turn the screw of the lamp room or lamp cap so that the light source point and the light inlet tube are on the same horizontal line until the brightness is uniform and reaches the maximum in the field of view.

(2) Adjustment of the mirror After the aperture of the field of view is narrowed, rotate the horizontal axis of the mirror, and its small round bright spot should move strictly parallel to the vertical line of the eyepiece crosshair, and then make the small bright spot located in the center of the field of view and evenly divided by the crosshair, which means that the position and inclination angle (45) of the mirror have been adjusted. It should be pointed out that in some new microscopes, the mirror is fixed on the horizontal axis (in the correct position) and cannot be adjusted by itself.

(3) The practice of adjusting the aperture stop and the field stop proves that due to the influence of glare, opening the large aperture stop inappropriately cannot effectively improve the resolution of the reflective objective. The appropriate size of the aperture stop (the image of the aperture stop can be seen on the back interface of the objective lens by removing the eyepiece or pushing in the Bohr lens) should change with the magnification of the objective lens. When using low power objective lens, the aperture pupil can be opened to basically coincide with the hole edge; When using medium and high power lens, it should be reduced appropriately (1/3 to 1/2).

The adjustment of the field stop is to reduce the aperture first and adjust it to the center of the crosshair. If the aperture boundary is blurred or red and blue, turn the field lens until the field boundary is clear and colorless. Open the aperture again to the periphery of the observation area, and don't open it again.

(4) Inspection and calibration of the vibration direction of the polarizer. Usually, the vibration direction of the polarizer is to place a piece of graphite or molybdenite on the stage, push out the polarizer on it and rotate the animal stage, so that the extension direction of the mineral crystal (high reflectivity direction) is in the brightest position, and its extension direction is the vibration direction of the front polarizer. If the extension direction of minerals is just parallel to the crosshair, the east-west direction proves that the polarizer in front is also east-west. Otherwise, it is necessary to make the mineral extension direction parallel to the crosshair, from east to west to back, and then rotate the front polarizer until the mineral is the brightest, at which time the front polarizer is in the east-west direction.

The way to check whether the two polarizers are strictly orthogonal is to first determine the position of the front polarizer with the above method, and then push the polarizer. If the mineral is the darkest (extinction), once the surface rotates, it will go out four times, and the distance between them is strictly 90. At the same time, the polarization color in each 45 direction should be exactly the same. Or use homogeneous minerals, such as pyrite, to observe the cone light under a high-power strain-free objective lens. If the polarization diagram is a perfect black cross, it can be proved that the two polarizations are orthogonal. In the above two inspection methods, if the fourth extinction interval of the former is not equal, and the image of the latter is slightly hyperbolic, it means that the two polarizations are not completely orthogonal. The upper polarizer must be carefully adjusted to meet the above requirements, and the calibration positions of the front polarizer and the upper polarizer should be recorded for future reference.

The correction of the center of the objective lens is the same as that of the polarizing microscope, and will not be described in detail.

2. General procedure for using mineral microscope

(1) Install vertical illuminators. Some vertical illuminators have been fixed on the lens barrel, and only need to adjust the illumination. The detachable vertical illuminator should be installed in the given position of the lens barrel.

(2) Installation of objective lens and eyepiece Due to different microscope models, the installation method of objective lens is also different. If there is a microscope, it should be inserted horizontally along the joint groove. The objective lens of some microscopes is installed by screwing on the spring clip. At present, the objective lens is mostly screwed on the objective joint of the lens barrel or on the turntable.

(3) Turn on the lighting and press the switch of the illuminator, and pay attention to adjust the brightness to a suitable level.

(4) Install the optical sheet on the stage, flatten the optical sheet on the stage with a proper amount of cement, then put it on the stage of the microscope, and then adjust the lens barrel or lift the stage to focus it.

3. Maintenance of microscope

(1) The screws of any parts or accessories are not allowed to move and twist at will, and the reasons (such as wrong direction, stuck or screwed to the limit) should be carefully identified and properly handled.

(2) Microscope components (such as objective lens and eyepiece). ) can't mix, the same model and different models of microscope can't mix.

(3) The storage temperature of the microscope should be appropriate, generally between -4℃ and +20℃, and it should not be too cold or too hot to avoid degumming and deterioration and failure of lubricating oil. Pay special attention to avoid exposing or baking heating equipment.

(4) The polarizer (especially the polarizer made of Iceland spar) should be gently pushed and pulled; The lens should also be lightly loaded and unloaded to avoid damage due to vibration strain and degumming.

(5) Dust has a great influence on the microscope, and its optical system should be kept strictly clean, but the objective lens should never be disassembled. All lenses and polarizers can't be wiped with fingers or ordinary paper and fabric, only the outer surfaces of objective lens and eyepiece lens can be gently wiped with mirror wiping paper or absorbent cotton.

(6) The plug of the low-voltage incandescent bulb must be plugged into the transformer, and it must not be directly plugged into the power supply to prevent the bulb from burning out. Light bulbs and transformers can't be powered on for a long time, so they should be turned off at intervals. In addition, if the transformer hums, it is necessary to unplug the transformer bolt from the power supply immediately for inspection.

experimental work

(1) Everyone uses some kind of microscope regularly. Read "Instructions for Use of Reflective Microscope".

(2) Focus on learning the structure and working principle of vertical illuminator, be familiar with the types of objective lens and eyepiece, as well as the use methods of front polarizer and upper polarizer, and understand and be familiar with the use and usage of aperture diaphragm and field diaphragm.

(3) Take galena (white) as the standard, and adjust the color of light with blue glass sheets to make it pure white. Pay attention to adjust the angle and position of the light source, remove obstacles, and make the light intensity reach its due brightness.

(4) Visit other types of reflective microscopes.