What is a microscope? Why do we need it? We all know that it is microorganisms that cause various diseases to us and other living organisms. But, how have you ever seen them with your naked eyes? Have you ever wondered how scientists can see microorganisms? Microorganisms are so tiny that we cannot see them with naked eyes, yet scientists have discovered a lot about them. Do you know how?

Which device was used in the early days to observe these tiny little organisms? Yes, it was a microscope. Not just microorganisms, microscopes have helped observe different objects under different subjects like animal or plant cells, tissues, vessels, fabrics, etc. You must have seen or even used this device in your biology laboratory to observe specimens. In this article, we will be learning about the invention of microscopes and their different types.

What is a Microscope?

The word ‘Microscope’ is made up of two Greek words, ‘Micro‘ meaning small and ‘Scope‘ meaning look or see. We can say that a microscope is an optical instrument that is used to see tiny objects that cannot be seen through naked eyes.

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For example, we can observe different microbes like bacteria, viruses, fungi, etc., through microscopes. Basically, microscopes create an enlarged image (magnify the image) of the tiny objects that we want to see with the help of lenses or certain kinds of radiation.

Microscopes are instruments devised to produce magnified visual or photographic representations of objects very small to be seen with the naked eye. Hence, the microscope must perform three important tasks:

1. Create a magnified image of the specimen.
2. Separate the small details in the image.
3. Present these details visible to the human eye or camera.

Fig: Microscope

History of Microscope

The earliest or simplest microscope was just a tube with a plate for the subject at one end and a lens that gives a magnification ten times the actual size. Compound microscopes were invented before the single-lens microscope. But, the instruments and materials that were used to make these were so poor that the results were very poor. There was a series of models of microscopes created in different years. Following are some of the well-known and important inventions of the microscope:

1. The smallest thing that humans could see for thousands of years was as wide as a hair strand. In 1590, two Dutch spectacle-makers and father-and-son teams, Hans and Zacharias Janssen, created the first microscope. This made it possible to see a new world of living things in the water, food, external organs, etc.
2. In 1609, Galileo Galilei improved the design of Hans and Janssen’s model of microscope and called his design occhiolino or little eye. 
3. The microscope was again improved by a British microscopist, Robert Hooke, in the 1660s, and he also explored the structure of snowflakes, fleas, lice, and plants. In 1665, he detailed all his observations in his book ‘Micrographia.’
4. In the 1670s, Dutch scientist  Anton Van Leeuwenhoek designed a single-lensed, high-power microscope that could magnify the image up to 270 times larger than the object’s actual size. 
5. In 1903, Richard Zsigmondy invented the ultramicroscope, which allows for observation of specimens below the wavelength of light. 
6. In 1932, a phase the contrast microscope was invented by Frits Xernike, which was used for the study of transparent biological materials. 
7. In 1938, Ernst Ruska developed the Electron Microscope. He realized that the use of electrons in microscopy could enhance resolution. 
8. In 1981, scanning tunnelling microscopes were invented by Gerd Binnig and Heinrich Rohrer, through which we can see3D images of specimens.

Invention of Microscopes

The high-tech microscopes that we are using now in our laboratories were not the same today. There were many versions produced over the years, and each version was recreated by adding new features and reducing the chances of errors that the previous microscope model had. Let’s take a look at some of the early microscopes invented by scientists.

Janssen Brother’s Compound Microscope: The Janssen brothers in the Netherlands and Galileo in Italy worked together and invented the compound microscope in the early 1600s. It was the simplest microscope. It consisted of two convex lenses aligned in series- an object-glass (objective) closer to the object or specimen and an eyepiece (ocular) closer to the observer’s eye. We could also adjust the position of the specimen and the microscope lenses.

Fig: Janssen’s Compound Microscope

Anton Van Leeuwenhoek’s Microscope

Anton Van Leeuwenhoek invented the simple microscope in the late 1600s. He was able to see single-celled animals or bacteria of similar size. To observe an object through it, one has to hold it close to the eye. The images produced by this microscope appear as they were on the same side of the lens as the object itself. An image that appears ten inches from the eye is known as a virtual image and cannot be captured on film.

Fig: Anton Van Leeuwenhoek’s Simple Microscope

Hooke’s Microscope The simple compound microscope shown in the picture below was invented by the British microscopist Robert Hooke in 1670.

Fig: Hooke’s Microscope

1. This microscope has an objective near the specimen. The objective can be focussed by turning the body of the microscope to move the objective closer or farther from the specimen.
2. An eyepiece lens is inserted at the top of the microscope. In many cases, an internal ‘field lens’ is inserted in the barrel of the microscope to increase the view field.
3. The microscope is illuminated by an oil lamp and spherical water reservoir/flask, as shown in the figure above. The light from the oil lamp gets diffused when passed through the water flask and is focussed on the specimen with the help of a lens attached to the water reservoir.
4. The main limitation of this microscope was a chromatic or spherical aberration. All the images observed in white light had “halos” either in red or blue colours.

Types of Microscopes

Microscopes have played a very important role in a detailed study of a wide range of specimens. There are varieties of microscope models used these days. Each of these has its own purpose. Some are useful in biological applications, and some are used in educational institutions. Few types of microscopes are useful in metallurgy and in studying three-dimensional samples. Some of the common types of microscopes are explained below:

1. Simple Microscope

A simple microscope can be defined as a microscope that uses a single magnifying lens (convex lens). This lens usually has a shorter focal length, and it magnifies the object through angular magnification. Therefore the image formed by this microscope is erect, virtual, and near the lens.

Fig: Simple Microscope

Principle of a Simple Microscope

If a tiny object is placed within the focus of the lens, then a virtual, erect, and magnified image is formed near the lens. This image can be seen through the naked eye by peeping through the lens.

Application of Simple Microscope

1. It is commonly used by the watchmaker to the smallest internal parts of the watch.
2. Most educational institutions like schools, colleges, universities use simple microscopes in their laboratories for educational purposes.
3. Jewellers also use it to observe the delicate parts and designs of the jewellery.
4. Skin specialists (Dermatologists) use simple microscopes to observe the skin and identify different skin diseases closely.

2. Compound Microscope

A compound microscope is a type of microscope that uses multiple lenses to enlarge the image of an object to be observed. It consists of a combination of lenses, i.e., it has two lenses- an objective lens (which is placed close to the object to be observed) and an eyepiece ocular lens (allows an image to be seen). A compound microscope is also called a Bright-field microscope.

Fig: Compound Microscope

Principle of Compound Microscope: A combination of lenses enhances the magnification of the object or sample. A beam of light is passed through the object to be observed. The objective lens captures the light beam passed by the object and creates a real and magnified image (primary image) of the object inside the body tube. The eyepiece or ocular lens again magnifies the image and creates a virtual image.

Applications of Compound Microscope

1. It is used in pathology labs to diagnose different diseases.
2. It is used in forensic laboratories to detect various crime cases and to solve them by drawing out human cells and observing them under a compound microscope.
3. Compound microscopes are also used in metallurgy to identify the presence or absence of certain minerals in metals.
4. It is also used in schools and colleges for conducting experiments in laboratories.
5. It is used to observe various microbes like bacteria, viruses, fungi, etc.

3. Electron Microscope

It is a type of microscope that uses a beam of accelerated electrons. It is a type of microscope that forms high-resolution images of objects.

Fig: Electron Microscope

Principle of Electron Microscope: A high voltage is applied to the tungsten metal present in an electron microscope, resulting in the excitation of electrons in a continuous stream used as a beam of light. Magnetic coils are used as lenses to focus the beam of electrons on the object to illuminate the object—the strength of the magnetic field increases as the flow of current increases.

There are two different types of electron microscopes:

1. Transmission Electron Microscope (TEM)
2. Scanning Electron Microscope (SEM)

Transmission Electron Microscope (TEM)

A transmission Electron Microscope (TEM) is used to view thin specimens (objects) by using a beam of electrons for illumination. TEM is similar to conventional (compound) light microscopes. TEM is used to image the structure of protein molecules, the interior of cells, the organization of molecules in viruses and cytoskeletal filaments, and the arrangement of protein molecules in cell membranes.

Fig: Transmission Electron Microscope (TEM)

Scanning Electron Microscope (SEM)

It depends on the emission of secondary electrons from the surface of the specimen (object). It provides detailed images of the surfaces of cells and whole organisms that are not possible with a Transmission Electron Microscope (TEM). It is also used for particle counting and size determination, and process control.

Fig: Scanning Electron Microscope (SEM)

Application of Electron Microscope

1. In the industries, electron microscopes are used for quality control and failure analysis.
2. Electron microscopes are also used to study metals and crystals.
3. It is also used to produce electron micrographs using specialized digital cameras and frame grabbers to capture the images.
4. The study of microorganisms is also done using electron microscopes.

Summary

A microscope is an optical instrument used to see tiny objects that cannot be seen through naked eyes. We can study different microorganisms like bacteria, viruses, and fungi using microscopes. Hans and Zacharias Janssen created the first microscope in 1590. There were different versions of microscopes invented by different scientists like the Hooke’s microscope invented by Robert Hooke, Leeuwenhoek microscope invented by Anton von Leeuwenhoek, Janssen compound microscope invented by Janssen brother. Each of them has tried to reduce the limitations of previous versions of microscopes.

Basically, there are three different types of microscopes- Simple microscopes, compound microscopes and electron microscopes. Electron microscope is further divided into two categories: Transparent Electron Microscope (TEM) and Scanning Electron Microscope (SEM). All these microscopes have a huge variety of applications in educational, research, industrial, and scientific fields.

Frequently Asked Questions (FAQs) on Invention of Microscope and Its Different Types

Q.1. Who invented the first microscope?
Ans: Two Dutch spectacle-makers and father-and-son teams, Hans and Zacharias Janssen, invented the first microscope in 1590.

Q.2. What was the limitation of Hooke’s Microscope?
Ans: The main limitation of Hooke’s microscope was a chromatic or spherical aberration. All the images observed in white light had “halos” either in red or blue colours.

Q.3. What is the difference between a simple microscope and a compound microscope?
Ans: Simple microscopes consist of a single lens to magnify the images. Compound microscopes consist of multiple lenses to magnify the images.

Q.4. What is the principle of a simple microscope?
Ans: If a tiny object is placed within the focus of the lens, then a virtual, erect, and magnified image is formed near the lens. This image can be seen through the naked eye by peeping through the lens.

Q.5. What are the applications of electron microscopes?
Ans: In the industries, electron microscopes are used for quality control and failure analysis. Electron microscopes are also used to study metals and crystals. It is also used to study microorganisms.

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