what is the major type of microscopes and their functions?

While most people picture the compound model from lab class when they think of microscopes, many types of microscopes are actually available.

These useful devices are employed by researchers, medical technicians and students on a daily basis; the type they select depends on their resources and needs. Some microscopes provide greater resolution with lower magnification and vice versa, and they range in cost from tens to thousands of dollars.

major type of microscopes and their functions

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 6 such microscope types that are discussed along with their diagram, working principle and applications. These six major types of microscopes are:

  1. Simple microscope
  2. Compound microscope
  3. Electron microscope
  4. Confocal Microscope
  5. Stereomicroscope
  6. Scanning probe microscope

1) Simple Microscope

The simple microscope is generally considered to be the first microscope. It was created in the 17th century by Antony van Leeuwenhoek, who combined a convex lens with a holder for specimens. Magnifying between 200 and 300 times, it was essentially a magnifying glass.

While this microscope was simple, it was still powerful enough to provide van Leeuwenhoek information about biological specimens, including the difference in shapes between red blood cells.

Today, simple microscopes are not used often because the introduction of a second lens led to the more powerful compound microscope.

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 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 arts 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.

2) Compound Microscope

With two lenses, the compound microscope offers better magnification than a simple microscope; the second lens magnifies the image of the first. Compound microscopes are bright field microscopes, meaning that the specimen is lit from underneath, and they can be binocular or monocular.

These devices provide a magnification of 1,000 times, which is considered to be high, although the resolution is low. This high magnification, however, allows users to take a close look at objects too small to be seen with the naked eye, including individual cells.

Specimens are usually small and have some degree of transparency. Because compound microscopes are relatively inexpensive yet useful, they are used everywhere from research labs to high school biology classrooms.

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. 

3) Stereo Microscope

The stereo microscope, also called a dissecting microscope, provides magnification of up to 300 times. These binocular microscopes are used to look at opaque objects or objects that are too large to be viewed with a compound microscope, since they do not require a slide preparation.

Although their magnification is relatively low, they are still useful. They provide a close-up, 3-D view of objects’ surface textures, and they allow the operator to manipulate the object during viewing.

Stereo microscopes are used in biological and medical science applications as well as in the electronics industry, such as by those who make circuit boards or watches.

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 the 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.

4) Confocal Microscope

Unlike stereo and compound microscopes, which use regular light for image formation, the confocal microscope uses a laser light to scan samples that have been dyed.

These samples are prepared on slides and inserted; then, with the aid of a dichromatic mirror, the device produces a magnified image on a computer screen. Operators can create 3-D images, as well, by assembling multiple scans.

Like the compound microscope, these microscopes offer a high degree of magnification, but their resolution is much better. They are commonly used in cell biology and medical applications.

5) 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.

6) 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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