Page 1 of 13

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.

Page 2 of 13

(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.

Page 3 of 13

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.

Page 4 of 13

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 doesn’t 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.

Page 5 of 13

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

Page 6 of 13

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 shapes of clear

glass and one of their samples was thick in the middle and thin on the edges. They

discovered that if you held one of these “lenses” over an object, the object would look

larger.

Someone also discovered that you can focus the rays of the sun with one of these

special “glasses” and start a fire. These early lenses were called magnifiers or burning

glasses. The word lens by the way, is derived from the latin word lentil, as they were

named because they resembled the shape of a lentil bean (look up lens in a dictionary).

These lenses were not used much until the end of the 13th century when spectacle

makers were producing lenses to be worn as glasses.

The early simple “microscopes” which were really only magnifying glasses had one

power, usually about 6X - 10X . One thing that was very common and interesting to look

at was fleas and other tiny insects. These early magnifiers were hence called “flea

Page 7 of 13

glasses”.

Sometime about the year 1590, two Dutch spectacle makers, Zaccharias Janssen and

his father Hans started experimenting with these lenses. They put several lenses in a

tube and made a very important discovery. The object near the end of the tube

appeared to be greatly enlarged, much larger than any simple magnifying glass could

achieve by itself! They had just invented the compound microscope (which is a

microscope that uses two or more lenses).

Galileo heard of their experiments and started experimenting on his own. He described

the principles of lenses and light rays and improved both the microscope and telescope.

He added a focusing device to his microscope and of course went on to explore the

heavens with his telescopes.

Anthony Leeuwenhoek of Holland became very interested in lenses while working with

magnifying glasses in a dry goods store. He used the magnifying glass to count threads

in woven cloth. He became so interested that he learned how to make lenses. By

grinding and polishing, he was able to make small lenses with great curvatures. These

rounder lenses produced greater magnification, and his microscopes were able to

magnify up to 270X!

Anthony Leeuwenhoek became more involved in science and with his new improved

microscope was able to see things that no man had ever seen before. He saw bacteria,

yeast, blood cells and many tiny animals swimming about in a drop of water. From his

great contributions, many discoveries and research papers, Anthony Leeuwenhoek

(1632-1723) has since been called the "Father of Microscopy".

Robert Hooke, an Englishman (who is sometimes called the “English Father of

Microscopy”), also spent much of his life working with microscopes and improved their

design and capabilities.

Little was done to improve the microscope until the middle of the 19th century when great

strides were made and quality instruments like today’s microscope emerged. Companies

in Germany like Zeiss and an American company founded by Charles Spencer began

producing fine optical instruments.

Today, there are no microscope manufacturers in the US and most of the microscopes

come from Germany, Japan and China. Toy plastic microscopes should be avoided as

they do not achieved the level of quality of the basic instruments with metal frames and

glass lenses.

Because of foreign production, quality microscopes have become affordable for all.

Zaccharias Janssen, the inventor of the microscope would marvel at the quality of even

Page 8 of 13

the most basic microscopes found in schools today.

Page 9 of 13

Page 10 of 13

Page 11 of 13

Page 12 of 13

Page 13 of 13