Types of Microscopes

Microscopes are essential tools in various scientific fields for observing objects and specimens at the microscopic level. There are several types of microscopes, each designed for specific applications and offering unique capabilities such as Optical Microscope, Compound Microscope, Electron Microscope, and Scanning Probe Microscope etc.

In this article, we will learn about various Types of Microscopes including their working principles as well as application in the real world.

What is a Microscope?

A microscope is a scientific instrument used to magnify and observe objects or specimens that are too small to be seen with the naked eye. It is a very useful tool for microbiologists and scientists involved in research and investigations.

Basic principle of a microscope involves the use of lenses or other optical systems to magnify the image of a specimen, allowing for detailed examination and analysis. Microscopes come in various types, ranging from simple optical microscopes, which use visible light to magnify images, to more advanced electron microscopes, which use beams of electrons to achieve much higher levels of magnification and resolution.

Who Invented Microscopes?

Invention of the microscope can be credited to many individuals throughout history, each contributing to its development and improvement over time. In the late 1500s, Dutch brothers Zacharias and Hans Janssen made the first documented compound microscope with two lenses. Then, in the 1600s, Antonie van Leeuwenhoek, also Dutch, used simple microscopes with one lens to look at tiny living things like bacteria and sperm.

Different Types of Microscopes

Microscopes are essential tools in science and medicine for magnifying and observing objects that are too small to be seen with the naked eye. There are several types of microscopes, each designed for specific purposes and offering different levels of magnification and resolution. Here are some common types of microscopes:

• Light Microscopes
  • Compound Microscope
  • Stereo Microscope (Dissecting Microscope)
  • Phase-Contrast Microscope
  • Fluorescence Microscope
  • Confocal Microscope
• Electron Microscopes
  • Transmission Electron Microscope (TEM)
  • Scanning Electron Microscope (SEM)
  • Scanning Transmission Electron Microscope (STEM)
  • Environmental Scanning Electron Microscope (ESEM)
• Scanning Probe Microscopes(SPM)
  • Atomic Force Microscope (AFM)
  • Scanning Tunneling Microscope (STM)
• Other Specialized Microscopes
  • X-ray Microscopes
  • Acoustic Microscopes
  • Electron Holography Microscopes

Let’s discuss these types in detail as follows:

Light Microscopes

Light microscopes are a type of microscope that use visible light and lenses to magnify and view small objects. They are also referred to as Optical Microscopes. These are the oldest kind of microscope which are still being used. In light microscopes, visible light is used to illuminate the object. The object is placed opposite an objective lens and the user sees it through an eyepiece lens. Light microscopes can magnify an object only upto 1000x due to limited resolving power of visible light.

Working Principle of Light Microscopes

Working principle of Light or Optical microscope is:

1. Consider an object AB. Light below the object illuminates it.
2. An objective lens PR placed close to the object produces a real and magnified image A’B’ between the objective lens and the eyepiece.
3. The eyepiece looks at that real image and produces a virtual image A”B” that is further magnified.
4. The final image that is seen through the eyepiece is inverted and highly magnified.

Types of Light Microscope

Common types of light microscopes are:

• Compound Microscope
• Stereo Microscope (Dissecting Microscope)
• Phase-Contrast Microscope
• Fluorescence Microscope
• Confocal Microscope

Now, let’s delve into these types with thorough detail.

Compound Microscope

A Compound microscope uses two lenses called as objective lens and eye piece. An objective lens produces a real image and magnifies the object. The eye piece, using the image created by the objective lens, further produces a highly magnified image. Higher magnification is attained by using two lenses rather than a single lens system.

Read More about Compound Microscope.

Stereo Microscope (Dissecting Microscope)

A stereo microscope, also known as a dissecting microscope or stereomicroscope, is a type of optical microscope that provides a three-dimensional view of specimens at low to moderate magnifications. The three dimensional view is provided using two objective lenses and eyepieces respectively. Therefore, two separate light paths are created, thus giving a 3D view to the eye.

Phase-Contrast Microscope

As the name suggests, Phase-Contrast Microscope uses the phase-shifts of visible light to brighten the areas in an object which were earlier partially or not visible. The phase shifts in light occurs when it passes through unstained living cells or other transparent specimens. These phase shifts are normally unnoticed by the human eye.

These phase-shifts in light are converted into changes in image brightness. Where the light is in-Phase, image is brighter and when it is Out-of-phase, the image is darker. This is achieved by analysing both direct rays and refracted rays. When the differences in image brightness are amplified, it enhances Contrast.

Fluorescence Microscope

A fluorescence microscope utilizes fluorescence or phosphorescence to observe and analyze specimens. Unlike traditional optical microscopes, fluorescence microscopes use fluorescence emitted by specific molecules within the specimen to generate high-contrast images. It uses a high-intensity light source that excites a fluorescent molecule in the specimen. It can be used to study the properties of both organic and inorganic substances.

Confocal Microscope

Confocal microscope is an advanced optical microscope that produces very high resolution images of organic and inorganic samples. In fluorescence microscopes, the entire specimen is flooded evenly with light, resulting in a large unfocused background whereas a confocal microscope uses point illumination and a pinhole to eliminate out-of-focus signal. This is achieved by using LASER of various colors to scan across the specimen.

Similar to the fluorescence microscope, the confocal microscope also uses fluorescence. Instead of illuminating the whole sample at once, laser light is focused onto a defined spot at a specific thus emitting fluorescent light at single point. A pinhole cuts off signals that are out of focus, thus allowing only the fluorescence signals from the illuminated spot to be visible.

Read more about Difference Between Simple And Compound Microscope.

Electron Microscopes

An electron microscope (EM) is a type of microscope that uses an electron beam as a light source. It uses electron optics, which are similar to light microscope lenses, to guide the electron beam.

Electron microscopes can be used to examine the ultra-structural structure of a broad variety of biological and non-biological samples, including microorganisms and cells, large molecules and biopsy samples, as well as metals and crystals. Electron microscopes are also commonly used in industrial settings for quality assurance and failure analysis.

Working Principle of Electron Microscopes

Working principle of electron microscopes is:

• The Electron Source emits a stream of high-voltage electrons (typically 5-100 keV) and accelerates them in a vacuum towards the sample using electrical potentials.
• The stream is condensed into a thin, single-colored, focused electron beam by using electromagnetic lenses and directed onto the sample by means of magnetic lenses.
• Interactions between the irradiated sample and the primary electron beam influence each other and produce products like secondary electrons or X-rays.
• The products of these interactions are identified and converted into an image.

Types of Electron Microscope

Electron Microscopes come in various forms, such as:

• Transmission Electron Microscope (TEM)
• Scanning Electron Microscope (SEM)
• Scanning Transmission Electron Microscope (STEM)
• Environmental Scanning Electron Microscope (ESEM)

Following this, we’ll take a closer look at each type, examining their characteristics in detail.

Transmission Electron Microscope (TEM)

It is the original type of electron microscope and uses a narrow but high voltage electron beam to illuminate the object and create an image. The beam of electron is created using an electron gun.

The beam is focused on electromagnetic lenses and transmitted through the object. The beam, once it emerges out of the object, carries information about its structure which is converted into an image. TEM typically magnifies an object upto 50 million times.

Scanning Electron Microscope (SEM)

Scanning Electron Microscope or SEM uses a focused electron beam to scan across the specimen called as raster scanning. When the beam collides with the object, it loses some of its energy which is converted into other forms such as X-ray or secondary electrons. These alternative signals carry information about the structure of the object. The varying intensities of these signals is converted into high-resolution object image.

The image resolution of a SEM is lower than that of a TEM. In SEM thick samples of the object can be used contrary to TEM which is able to scan only thin specimens.

Scanning Transmission Electron Microscope (STEM)

It is a type of Transmission Electron Microscope. In STEM, a very fine electron beam is scanned over the specimen,keeping it parallel to optical axis, so that the entire object is illuminated. The resultant image is a raster image of the object. STEM is useful for high-resolution imaging and elemental mapping.

Environmental Scanning Electron Microscope (ESEM)

Environmental Scanning Electron Microscope (ESEM) is a type of Scanning Electron Microscope that has the advantage that an object can be scanned in its natural environmental state ie even when it is wet and uncoated. There is little to no specimen preparation required before scanning.

Scanning Probe Microscopes(SPM)

Scanning Probe Microscope is a type of microscope that is used for studying surfaces at the nanoscale level. It uses a physical probe, which comes in contact with the specimen to study it. It makes use of the electrical current between the probe and the surface of the sample to generate its image.

This means that the object to be scanned should be conducting in nature. Due to this factor, only limited samples can be studies using a Scanning Probe Microscope. They have the capability to provide atomic level resolutions. The resolution however depends upon the probe and the sample being scanned. SPM too does not require much time and efforts for sample preparation.

Working Principle of Scanning Probe Microscopes

We can understand the working principle of scanning probe microscopes as follows:

• The operation of SPM is based on the interaction between the probe and the surface of the specimen.
• The probe is designed to be as fine as possible typically ending at a single atom.
• The probe is brought in contact with the surface of the sample , and the interaction between the probe and the sample surface is noted.
• The probe then scans the surface of the sample, and the interaction is measured at each point.
• The data collected is used to create an image of the sample.

Types of Scanning Probe Microscopes(SPM)

Some types of Scanning Probe Microscopes(SPM) include:

• Atomic Force Microscope (AFM)
• Scanning Tunneling Microscope (STM)

We’ll now discuss these types more thoroughly.

Atomic Force Microscope (AFM)

Atomic Force Microscope or AFM typically measures the forces between the probe and the sample to analyse various characteristics of the specimen. It can also be utilised to generate topographical imaging of the sample. It is a high-resolution, non-optical microscope and can produce images to a fraction of nanometers.

The basic operation involves moving the probe with a fine tip, over the sample surface. As the tip scans the features with varying heights, these variations are recorded to produce a three-dimensional topographic image of the sample. It can operate in various modes, including contact mode, non-contact mode and dynamic contact mode.

Scanning Tunneling Microscope (STM)

Scanning Tunneling Microscope or STM is another ground-breaking development in the field of imaging. It is a very high-resolution Scanning Probe microscope which can distinguish features with width less than 0.1 nm. Using STM, individual atoms can also be scanned and imaged. It works on the principle of Quantum Tunneling.

A very fine probe is brought close to the sample surface and a voltage is applied, an electron tunnel forms between the probe and the sample surface. These microscopes are generally built to be operated in vacuum due to the requirement of forming an electron tunnel.

Other Specialized Microscopes

Apart from the various microscopes described above, there are specialized microscopes built for specific applications and limited usage. Some of them are:

• X-ray Microscopes
• Acoustic Microscopes
• Electron Holography Microscopes

Next, we’ll explore each of these types in depth.

X-ray Microscopes

X-ray microscopes which we commonly know as X-ray machines used in various hospitals uses X-ray, an electromagnetic wave to form a contrast image of the object. The image is generally produced using a special film or a Charge Coupled Device(CCD). X-rays are short-wavelength and high energy radiations and are able to penetrate through maximum objects without getting reflected or refracted.

Also, because of their high energy, X-rays have the ability to penetrate relatively deep into objects, allowing images which can easily show internal structures.

Acoustic Microscopes

Acoustic microscope, as the name suggests, employs sound waves, particularly HF or UHF Ultrasound waves to detect hidden features inside materials and objects. Just as in case of light microscopes where light is emitted, acoustic microscopes emit high frequency ultrasound waves between 5 MHz to 400 MHz to produce high resolution images.

These waves, upon colliding with an object, are either scattered, reflected or absorbed. The reflected waves are then used to produce the image of the object.

Electron Holography Microscopes

Electron holograph microscope are based on the formation of an interference pattern or “hologram” of equidistant fringes in the transmission electron microscope (TEM).

The underlying principle is to create interference patterns between an object wave and a reference wave to create object’s phase and amplitude. It is of two types viz. Off-axis and In-line Holography microscope. It has applications in materials science, semiconductor research, and nanotechnology.

How to Choose the Right Microscope?

Choosing the right microscope is an important task and is influenced by a number of factors as discussed in the succeeding paragraph.

• Magnification: Make a choice about the magnification level that is required to be achieved. For magnifications upto 1000x, light microscopes are a better choice. For magnifications upto nanometer level, electron microscopes seem to be preferred.

• Application: Selection of right type of microscope largely depends on its usage. Whether a microscope is to be used for medical research, forensics or educations largely define the selection of appropriate type.

• Type of Specimen: Decide upon what kind of specimen is to be used under the microscope, whether a thin sample or thick sample is to be used. Other factors such as staining, kind od sample viz organic or material also influence the selection of right microscope.

• Contrast Method: Majority of organic samples do not have intrinsic contrast capabilities. Thus scopes with capability to generate contrast are available. It is to be decided first whether phase contrast or fluorescence is suitable for a particular sample.

• Image Quality and Resolution: For resolutions to the tune of 0.1 nm, electron or scanning probes are more suitable whereas light microscopes are suitable for fairly higher resolutions. Similarly, decision is to be made if 2D or 3D imaging is required.

• Users: Selection of a suitable microscope depends also on its users. Students and research scholars who are generally beginners and inexperienced may want to start with a compound microscope and slowly graduate to more complex systems.

• Budget: Budgeting and cost play an important role in the selection of a microscope. light microscopes are the cheapest to start with due to their less complex build as compared to other types of microscopes such as Electron microscopes or Scanning Probe microscopes.

Applications of Microscopes

Microscopes have numerous applications across various fields due to their ability to magnify small objects and reveal details that are not visible to the naked eye. Some common applications of microscopes include:

• Biological Research: Microscopes are extensively used in biology to study cells, tissues, and microorganisms.

• Medical Diagnosis: In medicine, microscopes play a vital role in diagnosing diseases and conditions.

• Forensic Science: Microscopes are essential tools in forensic science for analyzing evidence collected from crime scenes.

• Material Science: Microscopes are used in material science to analyze the structure and properties of various materials at the microscopic level.

• Electronics and Semiconductor Industry: Microscopes are utilized in the electronics and semiconductor industry for inspecting integrated circuits (ICs), printed circuit boards (PCBs), and other electronic components.

Advantages of Various Types of Microscope

Some common advantages for any microscope in general are:

• Magnification of tiny objects
• High-resolution images for detailed observation
• Essential for scientific research and discoveries
• Used in medical diagnosis and treatment
• Valuable tools for education and quality control

Other than these advantages, each types had their own individual advantages which are discussed as follows:

Advanatages of Light Microscopes

Some of the most common advantages of light microscope are:

• Small and Portable
• Unaffected by magnetic fields
• Low cost and Budget-friendly
• Resolution upto 1000x
• Simple to Use and Operate

Advanatages of Electron Microscopes

One can find several advantages when using electron microscopes, such as:

• Good analysis of subcellular structures
• Produces detailed imagery with resolution 1000x more than light microscopes
• Allows greater field of depth
• Requires minimal sample preparation
• Upto 2 million times more magnification than light microscopes

Advanatages of Scanning Probe Microscopes

The use of scanning probe microscopes is often advantageous due to several reasons, including:

• Minimal Sample preparation
• Does not require partial vacuum
• Accurate height measurement at nanoscale
• Comparatively easy to operate
• More portable than an electron microscope

Limitations of Different Types of Microscope

Some of the most common disadvantages of any microscopes are:

• Expensive to purchase and maintain
• Require specialized training to operate
• Time-consuming sample preparation
• Limited field of view
• Potential damage to delicate samples

Also, disadvantages of individual types are discussed as follows:

Disadvantages of Light Microscopes

A few of the primary limitations associated with light microscopes include:

• Limited magnification(Only upto 1000x)
• Less depth of field
• Less resolution- 1 micron
• May involve complex illumination techniques

Disadvantages of Electron Microscopes

Commonly encountered disadvantages of electron microscope include:

• Expensive
• Bulky Equipment
• Needs extensive sample preparation
• Highly trained manpower required to operate

Disadvantages of Scanning Probe Microscope

Scanning Probe Microscope often come with a set of disadvantages, including:

• Very large equipment
• Able to generate only monochromatic images
• Expensive
• Samples limited to conductors and semi-conductors
• Affected by magnetic fields

Conclusion

In conclusion, microscopes are essential tools for science, medicine, industry, and education. Each type of microscope, whether traditional or advanced, has its own strengths for different tasks and samples. Together, these microscopes enable researchers, clinicians, educators, and professionals to explore the microscopic realm, leading to new insights and innovations.

Read More,

• Parts of the Microscope and Their Uses
• Resolving Power of Microscope and Telescope
• Image formation by Lenses

Types of Microscope FAQs

What are the 5 Main Types of Microscope?

The five main types of microscopes are:

1. Optical Microscope (Light Microscope)
2. Electron Microscope (Transmission and Scanning)
3. Confocal Microscope
4. Scanning Probe Microscope (AFM and STM)
5. Fluorescence Microscope

What are Parts of Microscope?

The main parts of a microscope include:

• Eyepiece (Ocular lens)
• Objective lenses
• Coarse focus adjustment knob
• Fine focus adjustment knob
• Illuminator or light source
• Arm
• Nosepiece (rotating turret for objective lenses)
• Revolving nosepiece (to switch objectives)
• Eyepiece tube (head)

What is Resolving Power of a Microscope?

Resolving power, also known as resolution, in a microscope is its ability to distinguish between two closely spaced objects as separate and distinct.

What is Magnification in Microscope?

Magnification in a microscope refers to the degree to which an object appears larger when viewed through the microscope compared to when viewed with the naked eye.

What is Resolving Power of a Microscope?

Resolving power of a microscope, also known as resolution, is its ability to distinguish between two closely spaced objects and show them as separate and distinct entities.

What is Field of View(FOV)?

FOV or field of view is the maximum area visible through the eyepiece. When the magnification increases, FOV decreases.