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    Types of Microscope: Optical and Electron

    Microscope (With Figure)

    Microorganisms are usually not visible to naked human eye. They can be made visible, only

    when they are magnified under microscopes. Microscopes are instruments, which can produce

    enlarged images of very small objects, making it possible to view them, which, otherwise, cannot

    be seen distinctly by naked human eye. Different types of microscopes are used by the

    microbiologists for specific purposes. Microscopes are of the following types (Figure 4.1).

    A. Light or Optical Microscopes: In light or optical microscopes, light waves are used to produce the enlarged images of very small objects and magnification is obtained by a

    system of optical lenses. Ordinarily, microbes do not absorb much light, but staining

    them with dyes greatly increases their light absorbing ability, resulting in greater contrast

    and color differentiation.

    B. Light microscopes are of four types as described below:

    (1) Bright-field Microscope:

    In a bright-field microscope, the microscopic field (the circular area visible under microscope) is

    brightly illuminated and the microbes (or biological specimen) appear darker, as they absorb

    some of the light passing through them.

    It is of two types as follows:

    (a) Simple Microscope:

    A simple microscope is used to obtain small magnifications. A single biconvex lens magnifies

    the size of the object to get an enlarged virtual image.

    http://www.yourarticlelibrary.com/wp-content/uploads/2014/02/clip_image002146.jpg

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    (b) Compound Microscope:

    The most commonly used microscope for general purposes is the standard compound

    microscope. It magnifies the size of the object by a complex system of lens arrangement. It has a

    series of two lenses; the objective lens and the ocular lens, to magnify the size of the object.

    2. Dark-field Microscope: In a dark-field microscope, the object is brilliantly illuminated

    against a dark background.

    3. Fluorescence Microscope: It is used to view fluorescent microbes and microbes stained with

    fluorescent dyes for specific purposes.

    4. Phase-contrast Microscope: With a phase-contrast microscope, the differences among

    various cells with different refractive indices or thickness can be seen in unstained condition.

    Unstained structures within cells, not discernible by most other microscopes can also be

    observed, due to the slight differences in their refractive indices or thickness. It is a compound

    microscope fitted with a phase-contrast condenser and a phase-contrast objective.

    B. Electron Microscopes: In electron microscopes, electron beams are used to produce the

    image of the object and magnification is obtained by a system of electromagnetic fields, unlike

    in light microscopes, in which Tight waves are used to produce the image of the object and

    magnification is obtained by a system of optical lenses.

    The resolving power of electron microscopes is 200 times greater than that of light

    microscopes. They can produce useful magnifications up to X 400,000, as compared to X 2000

    in light microscopes. Thus, the useful magnification is 200 times greater in electron

    microscopes than in light microscopes.

    Electron microscopes are of three types as described below:

    1. Transmission Electron Microscope (TEM): In this microscope, electron beam is transmitted

    through an ultra-thin section of the object and the image is magnified by the electromagnetic

    fields. It is used to observe finer details of internal structures of microscopic objects like bacteria

    and other cells.

    2. Scanning Electron Microscope (SEM): This microscope uses an electron beam to scan the

    surface of the object, thereby inducing it to release a shower of electrons, which are collected by

    a detector to generate the image. It is used to observe the surface structure of microscopic

    objects.

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    3. Scanning and Transmission Electron Microscope (STEM): 3. Scanning and

    Transmission Electron Microscope (STEM):

    It has both transmission and scanning electron microscope functions.

    The Different Types of Microscopes

    The invention of the microscope has brought about great inventions that have transformed the

    human race. This device is effective and very important in science because it provides

    opportunity for scientist to study natural elements that are not visible to the naked eye.

    There are different types of microscopes depending on the purpose for which it is intended.

    Microscopes can also be classified based on their image making physical principles, area of

    application and versatility. However, microscopes can be comfortable divided into two

    categories, light microscope and electron microscope. Below is a list of the major microscope

    types and their uses.

    Light or Compound Microscopes

    These types of microscopes are based on a simple principle of light and lens. A light source

    illuminates the object while the lens magnifies it so that it can be visible to the human eye for the

    purpose of studying or evaluating. Under this category are the simple microscope, compound

    microscope and the stereo microscope.

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    Simple Microscope

    This is one of the oldest microscopes that uses a single lens for magnifying any samples.

    However, this microscope has been regarded as primitive because of its less relevance in serious

    scientific work.

    Compound Microscopes

    This type of microscope operates on the same principle as the as the simple microscope. But the

    difference is that it makes use of two different optical parts for the magnifying of objects. The

    compound microscopes are the most commonly used in many laboratories because they are

    efficient, inexpensive, and can magnify objects as much as 2000 times the original size. They are

    used mainly for the study of cells, chromosomes and the DNA.

    Dissection or Stereo Microscope

    This is another member of the optical microscopes that makes use of light and lens. This

    microscope is different from other types of microscopes because it allows you to view objects in

    3D. It contains lens in different angles that provides a three dimensional viewing of objects for

    complete diagnosis.

    However, the stereo microscope doesnt have very strong magnifying power like the compound

    microscope, but can be very useful in studying of dissection parts of living organisms. It is used

    mainly in the field of medical science including forensics, fine repair, sorting, and microsurgery.

    Other types of optical microscopes that are not very common but still well used includes the UV

    microscope that makes use of UV light to observe objects, the inverted microscope that is used

    for viewing thick or large objects upside down, and the metallurgic microscope used by

    engineers and scientists for viewing the structure of metals, ceramic and plastic. There are also

    digital microscopes that make use of optical lens and CCD/CMOS sensors to magnify objects to

    about 1000 times. Digital microscopes are also good because they have a 2 million pixel camera

    that provides high quality recording of the objects in view, and is connected to a TV monitor for

    high resolution viewing or observation.

    Electron Microscopes

    These are the most advanced types of microscopes used in modern science. The electron

    microscopes are powered by a beam of electron that strikes any objects that comes to its path to

    magnify it. Electron microscopes are used for studying cells and small particles of matter, as

    wells as large objects. Types of electron microscopes include transmission, scanning and

    reflection electron microscopes.

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    Transmission Microscope

    Transmission microscopes are used for studying cells and tiny slices of microorganisms like

    viruses, after they have been stained with palladium and gold and placed upon a wire grid.

    Scanning Electron Microscope

    Scanning electron microscopes have lower magnifying power but can provide 3 dimensional

    viewing of objects. The image of the object is captured in black and white after being stained

    with gold and palladium.

    Reflection Electron Microscope

    Reflection electron microscopes also uses electron beams but is different from transmission and

    scanning electron microscopes being that it is build to detect electrons that have been scattered

    elastically.

    All types of microscopes are used based on their purpose and the results that the scientist or the

    observer is trying to achieve. There are other microscopes designed for specific use in different

    types of field or based on their source like the X-ray microscope that uses X-ray beams to create

    images of an object. And the scanning acoustic microscope that makes use of sound waves to

    detect images. This type of microscope is used material science and biological science for

    detecting cracks in material and to uncover elasticity and stress in biological structures

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    respectively.

    History of the Microscope

    (includes: Who invented the microscope)

    During the 1st century AD (year 100), glass had been invented and the Romans were

    looking through the glass and testing it. They experimented with different