Types Of Microscopes | Uses And Their Applications

November 2, 2021

Microscope classification

There are different classes of microscopes, depending on their configuration, characteristics, lighting systems, and elements used for obtaining images. In summary, we carry out a classification of the different types of microscopes according to the latest advances in the field of microscopy.

Simple microscope

Loupes: monoculars and binoculars

Compound microscope

Stereoscopic, ultraviolet light, fluorescence, phase contrast, dark field, polarization and reflected light microscopy.

Electron microscopy

Scanning (SEM), Transmission (TEM), laser scanning confocal microscope.

OPTICAL MICROSCOPY

Simple microscope

They are provided with a converging lens or lens system arranged in such a way as to provide a virtual, right and magnified image of the sample, which in turn is located between the lens and the focus. Simple microscope magnification is limited and is often used for dissection of small animals, or for dissociation of histological specimens. These microscopes, also called loupes, can be monocular or binocular.

Light field optical microscope

The observation area of ​​this type of microscopes. it is brightly lit and the samples being examined appear darker than the background; they usually reach up to 1000x, with higher power eyepieces the magnification can be doubled. The useful limit is 2000x and is due to the resolution power, understood as the ability to distinguish two adjacent points as distinct and separate.

Lighting system

This resolving power is given as a function of the wavelength of the light used, and the numerical aperture of the set of lenses. Thus, it can be said that higher magnification is not always the most suitable, since they may not have sufficient sharpness with lower magnifications.

Upright microscope

It is the conventional microscope, perfected from old models; It has the light source at the base, below the stage. The optics in upright microscopes offer remarkable performance and provide sharp images throughout the amplification range; high numerical aperture and working distance combine for fast, uncomplicated observations. It is the most commonly used microscope.

Olympus BH 2 vertical research microscope

Inverted microscope

The structure of the microscope is inverted compared to the conventional microscope. The light source is located above the stage, and the operating and imaging system is the same as with the traditional microscope. It allows observing organisms or tissues in cell cultures as living cells without prior preparation, favoring the monitoring of growth status, behavior and other parameters involved in the development of the culture.

Inverted microscope  , stir and objectives below the stage. The light source is located at the top.

Microscopes according to the illumination system

At a basic level we can differentiate microscopes according to the medium used to illuminate the sample. The most common system is to illuminate the sample with visible light, leading to the optical microscope. However, there are alternatives.

1) Optical microscope

In the optical microscope the sample is illuminated by visible light. This means that there is a spot of light pointing towards the sample. That same light is conducted through the objective and the eyepiece until it forms the image in the observer’s eye. This is the most common type of microscope, but its resolution is limited by the diffraction of light. The maximum magnification that can be obtained with this type of microscope reaches around 1500x.

2) Electron microscope

In the electron microscope the sample is not illuminated with light but electrons are used  . The electrons impact the sample within a  vacuum chamber . There are different types of electron microscope but their principle of operation is always based on capturing the electrons scattered or omitted by the sample and thus being able to reconstruct an image.

The main advantage of this type of microscope is that a much higher magnification level can be obtained  than  other microscopes. However, it is necessary to prepare the sample and place it in a vacuum chamber so that it is not possible to observe live biological samples. The two main types of electron microscopes are the  scanning electron microscope  and the  transmission electron microscope .

3) Ultraviolet light microscope

The  microscopes ultraviolet light  illuminate the sample, as the name suggests, with  ultraviolet light . This type of light has a shorter wavelength than the visible light used in optical microscopes. The main advantage of using this technique is that better resolution can be achieved   than with visible light. In addition, the contrast obtained in the sample is different than in optical microscopes. In this way, with the ultraviolet light microscope they can observe samples that appear transparent if they are observed with visible light.

4) Polarized light microscope

Also known as a  petrographic microscope . This microscope is actually a type of light microscope to which two polarizers have been added  . This means that the light wave used to observe the sample has a specific direction of oscillation. This type of microscope is very useful for observing  crystalline structures  of rocks and minerals.

5) Fluorescence microscope

The  fluorescence microscopes  are those using fluorescence properties to generate an image of the sample. This microscope makes it possible to observe substances that emit  their own light  when they are illuminated with a certain wavelength. For this, the sample is usually illuminated with a  xenon lamp  or with a  mercury vapor lamp . These microscopes also incorporate light filters to isolate the light corresponding to the sample.

Sample observed in a fluorescence microscope (Source: Zeiss Microscopy)

Microscopes according to the number of lenses

In the specific case of the optical microscope, a distinction can be made according to the number of lenses in its optical system.

1) Simple microscope

This type of microscope has a single lens and is more commonly known as a  magnifying glass . Still, large magnifications can be achieved with a simple microscope. It should be noted that during the 17th century, Antonie van Leeuwenhoek used this type of microscope to achieve the highest magnification ever achieved. To this day, one of the concepts based on the same idea is the Foldscope.

2) Compound microscope

This type of microscope is one that has at least  two lenses . This is the most common case in all modern microscopes. Microscopes usually have different lenses on both the objective and the eyepiece to correct optical aberrations and achieve a good quality image. The invention of the microscope is associated with the invention of the compound microscope. This appeared in the Netherlands at the end of the 16th century.

Microscopes according to light transmission

There are two basic types of optical microscope depending on the path followed by the light to reach the objective: transmitted light microscopes and reflected light microscopes.

1) Transmitted light microscope

In this type of microscope,  light passes through the sample . For this class of microscopes it is necessary to prepare the sample by cutting it into very thin slices. The sample is illuminated from below the stage. The preparation of the sample makes it  semitransparent  and part of the light can pass through it and reach the objective to be observed later through the eyepiece. In general, this is the most widely used lighting system among optical microscopes.

2) Reflected light microscope

In this case the light illuminates the sample and part of it is reflected and directed to the objective. This requires illuminating the specimen from the top of the stage. This type of microscopy is used to examine  opaque materials such  as metallic structures, ceramic materials, etc. There are optical microscopes that allow both types of illumination so that it is possible to observe both semi-transparent and opaque samples. The stereoscopic microscopes (they allow to observe the sample in three dimensions) are always of reflected light.

Microscopes according to the number of eyepieces

Microscopes can also be classified according to the number of eyepieces. Based on this criterion, a distinction can be made between monocular, binocular or trinocular microscopes.

1) Monocular microscope

Monocular microscope

This type of microscope has a single eyepiece through which the sample can be observed. It is the simplest type and is ideal for microscopy hobbyists or someone new to this field. Its main disadvantage is that it can be a bit uncomfortable if it has to be used for long periods of time. For this reason monocular microscopes are generally not used in professional settings.

2) Microscopio binocular

Binocular microscopes have, as their name suggests, two eyepieces. This allows the sample to be observed simultaneously with both eyes resulting in greater comfort for the user. This is the most widely used type of microscope in research laboratories. The distance between the two eyepieces can be adjusted to suit the user’s needs. Do not confuse the binocular microscope with the stereomicroscope. The stereomicroscope is always binocular. However, not every binocular microscope is stereoscopic.

3) Trinocular microscope

The trinocular microscope is equipped with two eyepieces to view the sample plus a third eyepiece to connect a camera. In the case of connecting a digital camera, it can be connected to a computer to view the images of the sample in real time. With this microscope it is possible to observe the sample and at the same time take pictures or videos with the camera.

Microscopes according to the configuration of the elements

Inverted microscope (Source: Zeiss Microscopy)

Conventional microscopes have a vertical configuration. This means that the light source is at the bottom of the structure. Next there is the stage where the sample is placed and finally the head with the objectives and the eyepiece on top. This is the most common configuration but not the only one.

There are also inverted microscopes. These microscopes have a totally opposite configuration to that of the upright microscope. The sample is illuminated from the top and the optical elements are located under the stage. With this type of microscope it is possible to observe samples placed at the bottom of a container. This is very useful to keep them hydrated and thus be able to observe live samples and biological processes that last days.

Digital microscopes

Digital microscopes are those that capture a  digital image  of the sample. This is accomplished by connecting a digital camera instead of the eyepiece. There are digital microscopes with different configurations. Usually they must be connected to the  computer in order to transmit the images and then view them. It is also true that there are digital microscopes with a  built-in screen . These allow you to view the sample on the screen and store images that can then be transmitted to a computer via  USB connection  or  SD card .

A special type of digital microscopes are USB microscopes. These microscopes consist solely of a  high-magnification lens  and a  digital camera . The magnification that is achieved is limited compared to a conventional light microscope. Even so, they are very versatile and useful instruments for observing everyday objects. USB microscopes are connected to the computer via USB connection and allow images of the sample to be saved.

Stereoscopic microscope

The stereoscopic microscope is a type of microscope that allows you to observe the sample in a three-dimensional way  . These microscopes are always equipped with two eyepieces. The image of the sample that reaches each eyepiece is slightly different so that when they are combined, the 3D effect is achieved. This effect could not be achieved if the sample was viewed with only one eyepiece.

The magnification achieved with the stereomicroscope is lower than that achieved with a conventional optical microscope. However, conventional microscopes only allow two-dimensional observation of the sample. Stereomicroscopes are widely used in applications where the sample must be manipulated while observing. For example for the assembly of circuits or clocks.

Other types of microscopes

In addition to the microscopes presented above, there are a multitude of additional microscopy techniques optimized for specific sample types. Some of the ones worth mentioning are:

1) Microscopio confocal

This is a type  of fluorescence microscope . Instead of illuminating the sample globally, it is illuminated point by point in succession and the image is reconstructed at the end of the process. This process of scanning the sample is similar to that of scanning electron microscopes. This type of microscope was invented by  Marvin Minsky  in 1957.

2) Dark field microscope

This microscopy technique consists of illuminating the sample obliquely. In this way the light rays that reach the objective do not come directly from the light source but have been first scattered by the sample. This technique allows you to see samples that would not otherwise be visible due to their transparency. It also has the advantage that it does not require staining the sample to increase its contrast and be able to observe it.

Sample observed in a dark field microscope

3) Phase contrast microscope

Light travels at different speeds depending on the medium of propagation. This property is used in the phase contrast microscope since light passes through the sample with different speeds in different sections. This effect is amplified to generate the image of the sample. This technique does not require the use of dyes and therefore live cells can be observed. The phase contrast microscope was invented by  Frits Zernike  in 1932 and for this he received the Nobel Prize in Physics in 1953.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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