The bright field microscope or light microscope is a laboratory instrument used for the visualization of microscopic elements. It is a very simple instrument to use and it is also the most used in routine laboratories..
Since the appearance of the first rudimentary microscope created by the German Anton Van Leeuwenhoek, microscopes have undergone innumerable modifications, and not only have they been perfected, but different types of microscopes have also emerged.
The first brightfield microscopes were monocular, so it was observed through a single eye. Today microscopes are binoculars, that is, they allow observation through the use of both eyes. This feature makes them much more comfortable to use..
The function of the microscope is to magnify an image many times until it can be seen. The microscopic world is infinite and this device allows it to be explored.
The microscope consists of a mechanical part, a lens system and a lighting system, the latter powered by a source of electrical energy..
The mechanical part consists of a tube, the revolver, the macro and micrometric screws, the stage, the carriage, the holding clips, the arm and the base..
The lens system consists of the eyepieces and objectives. While the lighting system consists of the lamp, the condenser, the diaphragm and the transformer.
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The light or bright field microscope is very simple in its design, because in this case there are no light polarizers, or filters that can modify the passage of light rays as occurs in other types of microscopes..
In this case the light illuminates the sample from the bottom up; this passes through the sample and is then concentrated on the chosen objective, forming an image that is directed towards the eyepiece and that stands out in a bright field.
As brightfield is the most widely used type of microscopy, other types of microscopes can be adapted to brightfield..
The microscope consists of three well-defined parts:
Monocular microscopes have only one eyepiece, but binoculars contain two. They have converging lenses that magnify the virtual image created by the lens.
The eyepiece is made up of a cylinder that fits perfectly with the tube, allowing light rays to reach the magnified image of the objective. The eyepiece consists of an upper lens called the ocular lens and a lower lens called the collecting lens..
It also has a diaphragm and depending on where it is located it will have a name. The one located between the two lenses is called Huygens eyepiece, and if it is located after the two lenses it is called Ramsden eyepiece, although there are many others.
The magnification of the eyepiece ranges from 5X, 10X, 15X or 20X, depending on the microscope.
Through the eyepieces the operator will observe the image. Some models have a ring on the left eyepiece that is movable and allows image adjustment. This adjustable ring is called a Diopter ring..
They are in charge of increasing the real image that comes from the sample. The image is transmitted to the enlarged and inverted eyepiece. The magnification of the objectives varies. Generally, a microscope contains 3 to 4 objectives. Named from lowest to highest magnification are magnifying glass, 10X, 40X and 100X.
The latter is known as an immersion objective because it requires a few drops of oil to be used, while the rest are known as dry objectives. By turning the revolver you can go from one objective to another, always starting with the one with the lowest magnification.
Most lenses are imprinted with the manufacturer's marking, field curvature correction, aberration correction, magnification, numerical aperture, special optical properties, immersion medium, tube length, focal length, coverslip thickness, and color code ring.
Usually the lens has a front lens located at the bottom and a rear lens located at the top.
The lamp used for optical microscopes is halogen and they are generally 12 Volts, although there are more powerful ones. It is located at the bottom of the microscope, emitting light from the bottom up.
Its location varies according to the microscope model. It consists of a converging lens that, as its name suggests, condenses the light rays towards the sample..
This can be regulated by means of a screw and depending on the amount of light that needs to be concentrated, it can be raised or lowered..
The diaphragm acts as a regulator of the passage of light. It is located above the light source and below the condenser. If you want a lot of lighting it opens and if you need little lighting it closes. In this way it is controlled how much light will pass through the condenser.
This allows the microscope lamp to be powered by a power source. The transformer regulates the voltage that will reach the lamp
It is a hollow black cylinder through which the light beams travel until they reach the eyepiece..
It is the piece that supports the objectives, which are attached to it by a thread and at the same time it is the piece that allows the objectives to rotate. It moves from right to left and from left to right.
The coarse screw allows the target to be moved closer or further away from the specimen with grotesque movements of the stage vertically (up and down or vice versa). Some microscope models move the tube and not the stage.
When you are able to focus, you do not touch any more and you finish looking for the sharpness of the focus with the micrometer screw. In modern microscopes the coarse and fine screw come with a graduation.
Microscopes that have the two screws (macro and micro) on the same axis are more comfortable.
The micrometer screw allows extremely fine movement of the stage. The movement is almost imperceptible and can be up or down. This screw is necessary to adjust the final focus of the specimen.
It is the sample placement part. It has a strategically located hole to allow light to pass through the sample and the lens system. In some models of microscopes it is fixed and in others it can be moved.
The trolley is the piece that allows the entire preparation to be covered. This is extremely important, since most analyzes require the observation of at least 100 fields. Allows you to move from left to right and vice versa, and from front to back and vice versa.
These allow to hold and fix to the slide so that the preparation does not roll while the carriage is moved to travel the sample. It is located on the platen.
It is the place where the microscope must be grasped when moving from one place to another. This joins the tube to the base.
It is the piece that gives stability to the microscope; Allows the microscope to rest in a specific place without risk of falling. The shape of the base varies according to the model and brand of the microscope. Can be round, oval, or square in shape.
The microscope is highly useful in any laboratory, especially in the hematology area for the analysis of blood smears, red blood cell count, leukocytes, platelets, reticulocyte count, etc..
It is also used in the urine and feces area, both for the observation of the urinary sediment and for the microscopic analysis of the feces in search of parasites..
Also in the area of cytological analysis of biological fluids, such as cerebrospinal fluid, ascitic fluid, pleural fluid, joint fluid, spermatic fluid, urethral discharge and endocervix samples, among others..
It is also very useful in the area of bacteriology, for the observation of Gram stains of pure cultures and clinical samples, BK, India ink, among other special stains..
In histology it is used for the observation of thin histological sections, while in immunology it is used for the observation of flocculation and agglutination reactions..
In the research area it is very helpful to have a microscope. Even in areas other than health sciences, such as geology for the study of minerals and rocks..
The brightfield microscope allows a good perception of microscopic images, especially if they are stained.
Microscopes that use light bulbs are easier to use and much more comfortable.
It is not very useful for observing unstained samples. It is necessary that the samples are colored to be able to observe the structures with greater definition and thus they can contrast with the bright field.
It is not useful for the study of sub-cellular elements.
The magnification that can be achieved is less than that achieved with other types of microscopes. That is, when using visible light, the magnification range and resolution are not very high..
Mirrored microscopes require good external lighting and are more difficult to focus.
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