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# Types of Microscopes

## What are the Different Types of Microscopes?

There are different types of microscopes and each of these has different purposes of use. Some are suitable for biological applications, while others are used in educational institutions. There are also microscope types that find application in metallurgy and studying three-dimensional samples.

In this article, there are 5 such microscope types that are discussed along with their diagram, working principle and applications. These five types of microscopes are:

• Simple microscope
• Compound microscope
• Electron microscope
• Stereomicroscope
• Scanning probe microscope

## Simple Microscope

A simple microscope is defined as the type of microscope that uses a single lens for the magnification of the sample. A simple microscope is a convex lens with a small focal length. The magnifying power of the simple microscope is given as

 $$\begin{array}{l}m=1+\frac{D}{F}\end{array}$$

Where,

• D is the least distinct vision
• F is the focal length of the convex lens

### Principle of Simple Microscope

The working principle of a simple microscope is that when a sample is placed within the focus of the microscope, a virtual, erect and magnified image is obtained at the least distance of distinct vision from the eye that is held at the lens.

### Application of Simple Microscope

• It is common among the watchmakers as they can view a magnified image of the smallest parts.
• It is also used by the jewellers for obtaining a magnified image of the fine parts of the jewellery.
• Most educational institutions such as schools and colleges use a simple microscope in their laboratories.
• Dermatologists (skin specialists) use simple microscopes to identify different skin diseases.

## Compound Microscope

A compound microscope is defined as the type of microscope that has more than one lens. It has a combination of lenses and two optical parts known as an objective lens and an eyepiece or ocular lens. The magnifying power of the compound microscope is given as:

 $$\begin{array}{l}m=\frac{D}{f_{o}}\times \frac{L}{f_{e}}\end{array}$$

Where,

• D is the least distance of distinct vision
• L is the length of the microscope tube
• fo is the focal length of the objective lens
• fe is the focal length of the eyepiece

### Principle of Compound Microscope

The working principle of the compound microscope is that the combination of lenses enhances the magnification of the sample. The sample is first viewed as a primary image in the tube and viewed again in the eyepiece.

### Applications of Compound Microscope

• The study of bacteria and viruses is possible with the help of a compound microscope.
• A compound microscope finds application in forensic laboratories.
• It is also used in metallurgy.

## Electron Microscope

An electron microscope is defined as the type of microscope in which the source of illumination is the beam of accelerated electrons. It is a special type of microscope with a high resolution of images as the images can be magnified in nanometers.

There are two types of electron microscopes:

• The transmission electron microscope (TEM)
• The scanning electron microscope (SEM)

### Principle of Electron Microscope

The metal used in an electron microscope is tungsten. A high voltage current is applied which results in the excitation of the electrons in the form of a continuous stream that is used as a beam of light. The lenses used in the electron microscope are magnetic coils. These magnetic coils are capable of focusing the electron beam on the sample such that the sample gets illuminated. As the flow of current increases, the strength of the magnetic lens increases. The electron beam flow is designed such that it cannot pass through the glass lens.

### Application of Electron Microscope

• Quality control and failure analysis in industries are done with the help of an electron microscope.
• The images obtained in an electron microscope can be captured as electron micrographs with the help of specialized cameras.
• The study of metals and crystals became easy with the introduction of an electron microscope.

## Stereo Microscope

A stereo microscope is defined as a type of microscope that provides a three-dimensional view of a specimen. It is also known as a dissecting microscope. In a stereo microscope, there are separate objective lenses and eyepiece such that there are two separate optical paths for each eye.

### Principle of Stereo Microscope

A stereo microscope works on the reflected light from the sample. The magnification of the microscope takes place at low power and hence, it is suitable for magnifying opaque objects. It is suitable for thick and solid samples because it uses light reflected from the sample. The magnification of the stereo microscope is between 20x and 50x.

### Applications of Stereo Microscope

• Examination of historic coins and artefacts is possible with the help of the stereomicroscope.
• It finds application in microsurgery.
• Viewing of crystals became easy with the use of a stereomicroscope.

## Scanning Probe Microscope

The scanning probe microscope is defined as the type of microscope that finds applications in industries where the examination of the specimen is done at the nanoscale levels. The study of a specimen’s properties, its reaction time and its behaviour when stimulated can be done with the help of a scanning probe microscope.

### Principle of Scanning Probe Microscope

The scanning probe microscope has a probe tip that is mounted on the end of a cantilever. The tip is so sharp that it can move precisely and accurately across the surface of the sample scanning every atom. The tip is placed close to the surface of the sample, such that the cantilever experiences a deflection due to forces. This deflection distance is measured by the laser. The final image after scanning is obtained on the computer.

### Application of Scanning Probe Microscope

• It is used in studying different properties of the sample such as electrical properties.
• The magnetic property of the sample is studied using this microscope.
• The transferring of information on the sample can be done with the help of this microscope.

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## Frequently Asked Questions – FAQs

### What is the difference between low-powered and high-powered microscopes?

The basic difference between low-powered and high-powered microscopes is that a high power microscope is used for resolving smaller features as the objective lenses have great magnification. However, the depth of focus is greatest for low powered objectives. As the power is switched to higher, the depth of focus reduces.

### What is depth of focus in a microscope?

The depth of focus in a microscope is defined as the distance between the objective lens and the sample plane. The depth of focus varies from person to person and is also dependent on the quality of focus.

### What is the depth of field in a microscope?

The depth of field in a microscope is defined as the distance from the nearest object plane in focus to the farthest plane in the same focus. In microscopes, the depth of field is very short and is measured in units of microns.

### What is the field of view in a microscope?

The field of view in a microscope is defined as the diameter of the illuminated circle which is seen through the eyepiece. With an increase in the magnification, there is a decrease in the field of view.

### What is diopter adjustment?

The difference in vision between the two eyes is corrected with the help of diopter adjustment. Through diopter adjustment, the focus of the individual eyepiece can be done so that the eyes feel comfortable while observing the sample.

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