Forensic Physics
Types of Microscopes

Types of Microscopes

There are a lot of things, both living and non-living, on this earth and not everything is visible to the naked eye. Therefore, an instrument called a ‘microscope’ was developed to enter the world of those tiny things. 

The word ‘microscope’ is derived from the Greek words ‘mikros’ which means “small” and ‘skopein’ which means “to examine or look“. The first microscope developed was a simple microscope in 1590. It has been said that the first compound microscope was developed in 1620 in Europe but the founder is unknown.

Galileo Galilei discovered in 1610 that a telescope can also focus on small objects. He worked on it and his work was appreciated by Giovanni Faber, who named Galilei’s instrument a microscope in 1625. 

Since the variety of microscopic organisms or things is vast and they cannot be viewed by a single microscope. Therefore with the difference in the need for examining microscopic things, various types of microscopes were developed and still continue in the developing stage. 

Although there are various kinds of microscopes developed to date, each type has the same basic setup.

Components of Microscope

The components of microscopes are:

  • Light Source- This provides proper illumination for a clear view of any microscopic object.
  • Eyepiece– It is also known as an ocular piece which is a lens fitted at the top of a body tube through which a human views a microscopic object. Since it is close to the human eye, hence the name is the eyepiece.
  • Objective Lens– It is another lens fitted at the bottom of the body tube. This lens is placed near the microscopic object.
  • Condenser– A condenser is a lens that focuses light from thе illumination sourcе onto thе samplе. 
  • Stage– The object to examine is placed on the stage.

Types of Microscope

As discussed earlier, since there are different needs for every microscopic examination, therefore various types of microscopes have been developed. Some of them are:

1. Simple Microscope

It is also known as a single-lens microscope as it uses a single lens to focus light from the sample and magnify the image.

It is based on the principle that when an object is placed under a microscope, it produces a virtual, erect, and magnified image at the least distance of distinct vision from the eye that is held at the lens.

It was developed in the 17th century by Antony van Leeuwenhoek, who combined a convex lens with a holder for specimens. It magnifies the object between 200 and 300 times and it was more like a magnifying glass. Today these microscopes are not much in practice. They are only used by watchmakers, jewelers, etc.

2. Compound Microscope

It is today’s most basic microscope employed in every biological science field. The name is ‘compound’, as it combines two lenses for better magnification. The two lenses are the eyepiece and the objective piece.

It is based on the phenomenon of double magnification. The microscope forms a primary image in the tube which is then magnified by the eyepiece. It provides a magnification of 1,000 times, which is considered to be high, although the resolution is low. It is employed by each discipline of life sciences, where they examine bacteria, viruses, other pathogens, and many more such organisms. 

3. Stereo Microscope

It is also known as dissecting microscope. It is different from the above microscopes as it involves two separate objective lenses and eyepieces for each eye, hence it is a binocular microscope. It produces a three-dimensional image of the object.

It is usually employed for objects which are too large to be viewed in a compound microscope. Its magnification is 300 times. It is used in entomology to study the morphology and anatomy of insects. It is also used by the electronic industry to manufacture circuit boards or watches.

4. Phase Contrast Microscope

It is a contrast-enhancing optical technique that can be utilized to produce high-contrast images of transparent specimens. The phase contrast technique employs an optical mechanism to translate minute variations in phase into corresponding changes in amplitude, which can be visualized as differences in image contrast.

The important component of this instrument is the phase plate that is positioned in or very near the objective rear focal plane. It is used to study living cells, microorganisms, thin tissue slices, lithographic patterns, fibers, latex dispersions, glass fragments, subcellular particles, etc.

5. Polarising Microscope

It is a microscope that uses polarisation as the principal phenomenon for the image formation of an object. It uses a polariser and an analyzer as the important constituents of the microscope. The polariser allows only a certain light wave to pass through it, while the analyzer determines the amount of light and direction of light that will illuminate the sample.

Since the polarizer basically focuses different wavelengths of light onto a single plane, this microscope is perfect for viewing birefringent materials. It is used by geologists, petrologists, chemists, and the pharmaceutical industry to examine different rocks, minerals, chemicals, etc. Since these microscopes are utilized in studying rocks and minerals they are also referred to as ‘petrographic microscopes’.

6. Inverted Microscope

It is a compound microscope, upside down. In this instrument, the objective lens is placed beneath the sample stage, and the light source and condenser are on the top. It is primarily used for in-vitro fertilization, live cell imaging, developmental biology, cell biology, neuroscience, and microbiology.

It is also used in the metallurgy industry to examine large parts at high magnification for fractures or faults. One important feature of this microscope is that when it is used in the biological field, the sample is placed in a petri dish while in the metallurgy industry, the sample is analyzed by preparing a smooth side of the sample and placing it on the stage.

7. Fluorescence Microscope 

As the name suggests, this microscope uses fluorescence for image formation. The samples to be examined are either a fluorescent material or it is stained with a fluorescent dye. It uses two filters namely: the excitation filter (which filters the light before it reaches the specimen) and the Barrier or emission filter (which filters the light illuminated from the specimen). It is one of the most powerful tools to be used in the biomedical field.

8. Confocal Microscope

A confocal microscope uses a laser to illuminate the sample that has been dyed. The image produced is highly magnified, resolved, and three-dimensional. It uses point illumination (by focused laser beam) and a pinhole in an optically conjugate plane in front of the detector to eliminate an out-of-focus signal (confocal).

As a result, only light produced by fluorescence very close to the focal plane (in focus) can be detected. It is usually used in cell biology.

9. Comparison Microscope

It is a microscope that is used for the side-by-side comparison of two objects. It is a combination of two compound microscopes that are joined by an optical bridge. This combination results in a split view of the window which allows two separate objects to be viewed consecutively.

It is usually employed by forensic scientists to compare the various tool marks, handwriting, and firearm marks on the fired bullet and cartridges.

10. Electron Microscopes

This microscope uses a beam of electrons as an illuminating source for image formation. It is one of the most modern instruments developed for providing higher magnification and resolution. The two most widely used electron microscopes are the transition electron microscope (TEM) and scanning electron microscope (SEM).

Both TEM and SEM use electrons to create images, but the difference is that the image produced by TEM is two-dimensional while that of the SEM is three-dimensional. They are used in biological analysis, metallurgical analysis, nanotechnology analysis, and forensic analysis.

11. Digital Microscope

As with the advancement in technology, everything is going digital. So scientists have developed a new digital microscope, in which an optical microscope is attached to a digital screen. Different softwares are used to produce a magnified and highly resolved digital image on the screen.

It has a wide application in the fields of drug analysis, forensic analysis, metallurgical analysis, biomedical studies, etc. 

Conclusion

Microscopes have brought a revolution in examining objects or organisms that are not visible to the naked eye. They have let us study, analyze and discover a lot of unknown things. In the field of science, they have made every microscopic analysis so fast and easy that have helped this field to grow rapidly.

There are many types of microscopes that have been developed so far which are providing highly magnified and resolved images of objects using different illumination sources. There is still hope that in the future many more microscopes with advanced technologies will be developed which can help the various scientific fields to fill different gaps existing in the microscopy subject.

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