We explain piece by piece how this research device works.
Virtually everyone is familiar with the light microscope. It is common that during the classes taught for basic education, we are presented with the opportunity to handle one.
In this article we will cover all the parts of the common optical microscope, to improve our knowledge of its operation.
History of the light microscope
The light microscope is a fundamental basic tool in biological and medical research. Its invention came from a Dutch lens maker, Zacharias Janssen , in the 16th century. This microscope could only magnify images 9 times, but this early design was improved many times throughout history to allow us to study tiny things.
One of the best known scientists who popularized the use of the microscope was Antonie van Leeuwenhoek , also a Dutchman, in the 17th century. He himself made more powerful microscopes than the usual ones in his time (it is believed that he made microscopes with 500 magnifications, but those that have survived the passage of time only reach 275 magnifications), which allowed him to make discoveries such as the existence of bacteria, protists, or sperm . Thanks to his research, he is also known as “The Father of Microbiology”.
Light Microscope Parts
We can separate the parts that make up the optical microscope into two, depending on whether they participate in the optical system, which includes the lenses and light manipulation elements, or the mechanical system, which includes the rest of the parts that make it up.
Within the optical system, we will find these pieces according to the order in which light passes through them:
1. Focus
It is the light source of the microscope, located under the pieces that hold the sample. The light travels through the sample (from bottom to top) and its image reaches us through the rest of the parts of the optical system.
2. condenser
It concentrates and focuses the light beams that come from the focus on the sample.
3. Diaphragm
It is coupled to the condenser and allows to regulate the light that falls on the sample. This allows us to control the contrast of the sample and the depth of field (ie it helps us to focus at different heights within the sample).
4. Objective
The tubes that are placed on the sample, usually attached to the revolver (in case there is more than one). They are surely the most important part of the microscope and contain a series of lenses that allow us to increase the images and reduce the light aberrations that make it difficult to view the samples. The light passes directly through the objectives after passing through the sample.
Currently, the most commonly used objectives are 4, 10, 20, 40 and 100x (the notation “x” at the end of the number indicates the number of magnifications that the objective applies to the image). The highest magnification objective (100x) is usually the immersion objective, which should only be used after placing a small drop of oil between the sample and the objective (and cleaned before and after use).
This allows you to take full advantage of the magnification offered by the objective, since light undergoes greater refraction processes when traveling through air than through oil.
5. Eyepiece
The final piece of the optical system, where we place our gaze when operating the microscope. The eyepiece also has magnification. Microscopes today have two eyepieces, unlike early microscopes, which only had one. At least one of the eyepieces is adjustable and allows us to adjust the image to the diopter of the observer.
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In the mechanical system we will find the following parts :
6. Foundation
Also known as the foot, it is the part of the microscope that supports the rest of the structure and gives it stability.
7. Tube
It is the curved arm of the microscope that joins the base of the microscope with the optical system.
8. Platen
The horizontal platform on which we place the sample.
9. Clamps
The tweezers that hold the slide (the support where the sample is located).
10. Screws
There are two types of screw, which will be used depending on how much we want to move the sample:
- The macrometric screw, which offers us a greater movement and is usually used to place the sample in the initial focus, which is done with the lower resolution objective.
- The micrometric screw, which offers us a much smaller scale movement and is the one we will use when we are operating higher magnification objectives.
11. Stir
In cases where we have more than one objective, the revolver is the piece that allows us to rotate between the different objectives.
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conclusion
This analysis is limited to explaining the parts of the classical light microscope. Different types of microscopes are used in scientific research, depending on the size of what we need to observe. The electron microscope, for example, is used when what we are trying to study is below the theoretical physical resolution limit of an optical microscope, 0.2 micrometers.
Despite this limit, the classical light microscope remains the king of the biological laboratory and microscopy continues to advance with new technologies. Long live the microscope!
Bibliographic references
- Lane N. (2015). The unseen world: reflections on Leeuwenhoek (1677) ‘Concerning little animals’. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1666), 20140344.
- Wollman, AJ, Nudd, R., Hedlund, EG, & Leake, MC (2015). From Animaculum to single molecules: 300 years of the light microscope. Open Biology, 5(4), 150019.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.