Compound Microscope And Its Parts Pdf
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The microscope that you will use is called a compound microscope. You will need to know the names of some of its component parts:.
Before exploring the parts of a compound microscope , you should probably understand that the compound light microscope is more complicated than just a microscope with more than one lens. First, the purpose of a microscope is to magnify a small object or to magnify the fine details of a larger object in order to examine minute specimens that cannot be seen by the naked eye.
Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope. There are many types of microscopes, and they may be grouped in different ways. One way is to describe the method an instrument uses to interact with a sample and produce images, either by sending a beam of light or electrons through a sample in its optical path , by detecting photon emissions from a sample, or by scanning across and a short distance from the surface of a sample using a probe.
Microbiology, the branch of science that has so vastly extended and expanded our knowledge of the living world, owes its existence to Antony van Leeuwenhoek. In , with the aid of a crude microscope consisting of a biconcave lens enclosed in two metal plates, Leeuwenhoek introduced the world to the existence of microbial forms of life. Over the years, microscopes have evolved from the simple, single-lens instrument of Leeuwenhoek, with a magnification of , to the present-day electron microscopes capable of magnifications greater than , Microscopes are designated as either light microscopes or electron microscopes.
The former use visible light or ultraviolet rays to illuminate specimens. They include brightfield, darkfield, phase-contrast, and fluorescent instruments. Fluorescent micro-scopes use ultraviolet radiations whose wavelengths are shorter than those of visible light and are not directly perceptible to the human eye. Electron microscopes use elec-tron beams instead of light rays, and magnets instead of lenses to observe submicro-scopic particles.
This instrument contains two lens systems for magnifying specimens: the ocular lens in the eyepiece and the objective lens located in the nose-piece. The specimen is illuminated by a beam of tungsten light focused on it by a sub-stage lens called a condenser, and the result is that the specimen appears dark against a bright background.
A major limitation of this system is the absence of contrast between the specimen and the surrounding medium, which makes it difficult to observe living cells. Therefore, most brightfield observations are performed on nonviable, stained preparations.
This is similar to the ordinary light microscope; however, the condenser system is modified so that the specimen is not illuminated directly. The con-denser directs the light obliquely so that the light is deflected or scattered from the spec-imen, which then appears bright against a dark background. Living specimens may be observed more readily with darkfield than with brightfield microscopy. Observation of microorganisms in an unstained state is possible with this microscope.
Its optics include special objectives and a condenser that make visible cellular components that differ only slightly in their refractive indexes. As light is transmitted through a specimen with a refractive index different from that of the surrounding medium, a portion of the light is refracted bent due to slight varia-tions in density and thickness of the cellular components.
The special optics convert the difference between transmitted light and refracted rays, resulting in a significant vari-ation in the intensity of light and thereby producing a discernible image of the struc-ture under study.
The image appears dark against a light background. This microscope is used most frequently to visualize speci-mens that are chemically tagged with a fluorescent dye. The source of illumination is an ultraviolet UV light obtained from a high-pressure mercury lamp or hydrogen quartz lamp.
The ocular lens is fitted with a filter that permits the longer ultraviolet wavelengths to pass, while the shorter wavelengths are blocked or eliminated. Ultraviolet radiations are absorbed by the fluorescent label and the energy is re-emitted in the form of a different wavelength in the visible light range. The fluorescent dyes absorb at wavelengths between and nanometers nm and emit orange, yellow, or greenish light.
This microscope is used primarily for the detection of antigen-antibody reactions. Antibodies are conjugated with a fluorescent dye that becomes excited in the presence of ultraviolet light, and the fluorescent portion of the dye becomes visible against a black background. This instrument provides a revolutionary method of microscopy, with magnifications up to one million.
This permits visualization of submicroscopic cel-lular particles as well as viral agents. In the electron microscope, the specimen is illu-minated by a beam of electrons rather than light, and the focusing is carried out by elec-tromagnets instead of a set of optics.
These components are sealed in a tube in which a complete vacuum is established. Transmission electron microscopes require speci-mens that are thinly prepared, fixed, and dehydrated for the electron beam to pass freely through them. As the electrons pass through the specimen, images are formed by direct-ing the electrons onto photographic film, thus making internal cellular structures visi-ble.
Scanning electron microscopes are used for visualizing surface characteristics rather than intracellular structures A narrow beam of electrons scans back and forth, producing a three-dimensional image as the electrons are reflected off the specimen's surface. While scientists have a variety of optical instruments with which to perform routine laboratory procedures and sophisticated research, the compound brightfield micro-scope is the "workhorse" and is commonly found in all biological laboratories.
Although you should be familiar with the basic principles of microscopy, you probably have not been exposed to this diverse array of complex and expensive equipment. Therefore, only the compound brightfield microscope will be discussed in depth and used to examine specimens.
Practical use of the compound microscope for visualization of cellular morphology from stained slide preparations. Microbiology is a science that studies living organisms that are too small to be seen with the naked eye. Needless to say, such a study must involve the use of a good compound microscope. Although there are many types and variations, they all fundamentally consist of a two-lens system, a variable but controllable light source, and mechanical adjustable parts for determining focal length between the lenses and specimen.
A fixed platform with an opening in the center allows for the passage of light from an illu-minating source below to the lens system above the stage. This platform provides a surface for the placement of a slide with its specimen over the central opening. In addition to the fixed stage, most microscopes have a mechanical stage that can be moved vertically or horizontally by means of adjustment controls.
Less sophisticated micro-scopes have clips on the fixed stage, and the slide must be positioned manually over the central opening. The light source is positioned in the base of the instrument. Some microscopes are equipped with a built-in light source to pro-vide direct illumination. Others are provided with a mirror; one side flat and the other concave.
An external light source, such as a lamp, is placed in front of the mirror to direct the light upward into the lens system. The flat side of the mirror is used for artificial light, and the concave side for sunlight. This component is found directly under the stage and contains two sets of lenses that collect and concentrate light passing upward from the light source into the lens sys-tems.
The condenser is equipped with an iris diaphragm, a shutter controlled by a lever that is used to regulate the amount of light entering the lens system. Above the stage and attached to the arm of the microscope is the body tube. This structure houses the lens system that magnifies the specimen. The upper end of the tube contains the ocular or eyepiece lens.
The lower portion consists of a movable nosepiece containing the objective lenses. Rotation of the nosepiece posi-tions objectives above the stage opening. The body tube may be raised or lowered with the aid of coarse-adjustment and fine-adjustment knobs that are located above or below the stage, depending on the type and make of the instrument. To use the microscope efficiently and with minimal frustration, you should understand the basic principles of microscopy: magnification, resolution, numerical aperture, illumination, and focusing.
Enlargement or magnification of a specimen is the function of a two-lens system; the ocular lens is found in the eyepiece, and the objective lens is situated in a revolving nose-piece. These lenses are separated by the body tube. The objective lens is nearer the specimen and magnifies it, producing the real image that is projected up into the focal plane and then magnified by the ocular lens to produce the final image.
The most commonly used microscopes are equipped with a revolving nosepiece containing four objective lenses possessing different degrees of magnification. When these are combined with the magnification of the ocular lens, the total or overall linear magnification of the specimen is obtained. Although magnification is important, you must be aware that unlimited enlargement is not possible by merely increasing the magnifying power of the lenses or by using additional lenses, because lenses are limited by a property called resolving power.
By definition, resolving power is the ability of a lens to show two adjacent objects as discrete entities. When a lens cannot discriminate, that is, when the two objects appear as one, it has lost resolu-tion. Increased magnification will not rectify the loss, and will, in fact, blur the object.
The resolv-ing power of a lens is dependent on the wave-length of light used and the numerical aperture, which is a characteristic of each lens and imprinted on each objective.
The numerical aper-ture is defined as a function of the diameter of the objective lens in relation to its focal length. It is doubled by use of the substage condenser; which illuminates the object with rays of light that pass through the specimen obliquely as well as directly.
Thus, resolving power is expressed mathematically, as follows:. Based on this formula, the shorter the wave-length, the greater the resolving power of the lens. Thus, short wavelengths of the electromag-netic spectrum are better suited than longer wavelengths in terms of the numerical aperture. However; as with magnification, resolving power also has limits. You might rationalize that merely decreasing the wavelength will automati-cally increase the resolving power of a lens.
Such is not the case, because the visible portion of the electromagnetic spectrum is very narrow and borders on the very short wavelengths found in the ultraviolet portion of the spectrum.
The relationship between wavelength and numerical aperture is valid only for increased resolving power when light rays are parallel.
Therefore, the resolving power is dependent on another factor, the refractive index. This is the bending power of light passing through air from the glass slide to the objective lens. The refractive index of air is lower than that of glass, and as light rays pass from the glass slide into the air, they are bent or refracted so that they do not pass into the objective lens.
This would cause a loss of light, which would reduce the numerical aperture and diminish the resolving power of the objective lens. Loss of refracted light can be compensated for by interposing mineral oil, which has the same refractive index as glass, between the slide and the objective lens.
In this way, decreased light refraction occurs and more light rays enter directly into the objective lens, producing a vivid image with high resolution. Effective illumination is required for efficient magnification and resolving power. Since the intensity of daylight is an uncontrolled variable, artificial light from a tungsten lamp is the most commonly used light source in microscopy. The light is passed through the con-denser located beneath the stage.
The condenser contains two lenses that are necessary to produce a maximum numerical aperture. The height of the condenser can be adjusted with the con-denser knob. Always keep the condenser close to the stage, especially when using the oil-immersion objective. Between the light source and the condenser is the iris diaphragm, which can be opened and closed by means of a lever; thereby regulating the amount of light entering the condenser. Excessive illumination may actually obscure the specimen because of lack of contrast.
The amount of light entering the microscope differs with each objec-tive lens used. A rule of thumb is that as the mag-nification of the lens increases, the distance between the objective lens and slide, called working distance, decreases, whereas the numerical aperture of the objective lens increases. You will be responsible for the proper care and use of microscopes. Since microscopes are expensive, you must observe the following regu-lations and procedures.
The instruments are housed in special cabinets and must be moved by users to their laboratory benches. The correct and only acceptable way to do this is to grip the microscope arm firmly with the right hand and the base with the left hand, and lift the instrument from the cabinet shelf.
Carry it close to the body and gently place it on the laboratory bench.
Microscope Parts & Specifications
Though modern microscopes can be high-tech, microscopes have existed for centuries — this brass optical microscope dates to , and was made in Munich, Germany. A microscope is an instrument that is used to magnify small objects. Some microscopes can even be used to observe an object at the cellular level, allowing scientists to see the shape of a cell , its nucleus, mitochondria , and other organelles. While the modern microscope has many parts, the most important pieces are its lenses. A simple light microscope manipulates how light enters the eye using a convex lens , where both sides of the lens are curved outwards. When light reflects off of an object being viewed under the microscope and passes through the lens, it bends towards the eye. This makes the object look bigger than it actually is.
A compound microscope is a microscope that uses multiple lenses to enlarge the image of a sample. Typically, a compound microscope is used for viewing samples at high magnification 40 - x , which is achieved by the combined effect of two sets of lenses: the ocular lens in the eyepiece and the objective lenses close to the sample. Light is passed through the sample called transmitted light illumination. Larger objects need to be sliced to allow this to happen efficiently. Compound microscopes usually include exchangeable objective lenses with different magnifications e.
Historians credit the invention of the compound microscope to the Dutch spectacle maker, Zacharias Janssen, around the year more history here. The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope versus an electron microscope. The simplest optical microscope is the magnifying glass and is good to about ten times 10x magnification. Ocular eyepiece lens to look through. Objective lens, closest to the object. Before purchasing or using a microscope, it is important to know the functions of each part.
The eyepiece lens usually magnifies Any object you view through this lens would appear 10 times larger than it is. The compound microscope may contain.
Parts of Compound Microscope | Botany
Parts of the compound microscope Fig. These include base or foot, pillar, arm, inclination joint, stage, clips, diaphragm, body tube, nose piece, coarse adjustment knob and fine adjustment knob. It is the basal, horse shoe-shaped structure.
Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope. There are many types of microscopes, and they may be grouped in different ways.
Microbiology, the branch of science that has so vastly extended and expanded our knowledge of the living world, owes its existence to Antony van Leeuwenhoek. In , with the aid of a crude microscope consisting of a biconcave lens enclosed in two metal plates, Leeuwenhoek introduced the world to the existence of microbial forms of life. Over the years, microscopes have evolved from the simple, single-lens instrument of Leeuwenhoek, with a magnification of , to the present-day electron microscopes capable of magnifications greater than ,
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