Definition of Microscope
- A microscope is a laboratory instrument, which is used to examine or study or see objects that are too small to be seen by the naked eye.
- There are present different types of microscopes, such as; light microscopes, Electron microscopes, Scanning probe microscopes, Fluorescence microscopes, Super-resolution microscopes, and X-ray microscopes.
- Microscopes are creat an image of the sample or specimen and then send it as a beam of light or electrons to its optical path, or by scanning across, and a short distance from the surface of a sample using a probe.
- In the laboratory, Microscopes are used to visualize minute objects, for example; plant cell, animal cell, bacteria, fungi, etc.
- Microscopes consist of different types and numbers of magnifying lenses.
- A Microscopes are made up of two parts, the holding part which supports the microscopes and its components, and the optical part which is used for magnification and viewing of the specimen images.
Types of Microscopes
There are present mainly 3 types of Microscopes. They are classified based on their working principle and uses.
- Optical Microscopes: Optical Microscope Also Known as Light Microscope. There are present two types of optical Microscope such as;
- Simple microscope
- Compound microscope
- Electron microscopes: There are two main types of electron microscope;
- The Transmission Electron Microscope (TEM)
- The Scanning Electron Microscope (SEM)
- Scanning probe microscopes
Except for these three types, there are also present other types of microscopes such as X-ray microscopes, ultrasonic microscopes, etc.
General Working Principle of Microscopes
In a microscope, light rays first passed through the specimen and then is transmitted through two sets of lenses, the objective, which is nearest to the specimen, and the eyepiece, which is further away from the specimen.
The magnified image of the specimen is first produced by the objective. This is known as the primary image. The eyepiece then magnifies the primary image into the final one that is seen by the observer. The total magnification obtainable by the microscopes is the product of the magnification of the objective and that of the eyepiece. Examples are given below:
|Objective magnification||Eyepiece magnification||Total magnification|
Applications of Microscopes
- To study protein interaction or protein conformation.
- To Study the membrane dynamics.
- To study the concentration of calcium ion and pH changes.
- To Determine the shape of cells and intercellular structure.
- To determine the localization of specific proteins.
- To Study the Dynamics of protein.
- To study the iron concentration.
- Microscopes also used in forensic laboratories.
- Used in counting of blood cells.
Parts of a Microscope and Their Functions
The parts of a microscopes are divided into two main categories, such as;
- Structural parts of microscope
- Optical parts of microscope
Structural parts of Microscope and their Functions
The structural parts of microscope provide supports and connecting all the components of microscope. There are present three important structural parts of microscope such as;
It is located at the upper portion of microscope. The head portion of microscope is also known as the Body tube.
The head portion or body tube of microscope connects the eyepiece to the objective lenses.
It refers to the holding portion of a microscope, which is used to carry the microscopes.
Arm Supports the head or body tube and connects it to the base of the microscopes.
The bottom portion of Microscopes on which the arm portion is standing. It holds all the essential components.
The Base portion provides support to the microscope.
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Optical parts of Microscope and their Functions
The optical part of Microscope plays an important role to magnify the object. It consist of this following components;
- Eyepiece consists of two lenses, the ocular(The first one, near the eye) and eyepiece (The last one, away from the eye).
- This part of microscope is also known as ocular.
- Eyepiece is located at the top of the microscope.
- The magnifying power of an ocular lens varies from 5x to 30x, but normally 10X or 15X magnifying power is used.
- To get the total magnification level, multiply the magnification of the objective used (ex: 10X eyepiece * 40X objective = 400X total magnification).
Types of Eyepiece:
Several types of ocular are employed depending upon the kind of objective located on the microscope those most commonly used are;
In this type of eyepiece to simple Plano-convex lenses are employed the convex surfaces of both lenses face downward oculars in this group are spoken as negative eyepiece
Oculars of this type are referred to as hyperplane Planoscopic, periplane, etc. They may be employed with the high power achromatic, Fluorite, and apochromatic objectives without introducing chromatic aberrations in the image.
Ocular of this type consists of achromatic triplet combination of lens. These eye-piece are more perfectly corrected than are those of huygenion and hyperplane types.
- Help the viewer to see the magnified specimen.
- Helps to magnify the image of specimens.
- It corrects the defects of the objective.
2. Eyepiece tube
- It is located above the head portion.
- In binoculars, microscope Eyepiece tube is flexible and can for maximum visualization, for variance in distance.
- In monocular microscopes, the Eyepiece tube is none flexible.
- connects the eyepiece and ocular lens to the objective lenses
- Nosepiece is located below the Eyepiece tube.
- It is also known as a revolving turret.
- It can rotate to adjust the objective lens.
- It holds 2 -3 objective lense.
4. Objective lenses
- Objective lenses are located below the Nosepiece.
- Usually, you can find 3 or 4 objective lenses on a microscope.
- Commonly there are present 4 types of objective lenses with different magnification power such as 4X, 10X, 40X, and 100X.
- If we use a 4x Objective lens with a 10x eyepiece (most common), then the total magnification power will be 40x(4×10), In similarly way the total magnification power of other lenses will be 100x(10×10), 400x(40×10), and 1000x(100×10).
Types of Objective lenses:
There are three types of objective lens;
The achroma are the simplest in construction and the least expensive. The control of oberrations becomes more difficult when the power is increased.
This is also called semi apochromatic aberrations are largely eliminated by the use of flurite objectives.
This is the costly objective lens with respect to other lenses and it has the power to correct aggeration highly perfect.
- Helps to increase the magnification levels of specimen image.
- Together the light rays coming from any point of the objects.
- To unite the light at a point of the image.
5. The Adjustment knobs
- The Adjustment knobs are located over the Objective lenses.
- There are two Adjustment knobs such as Coarse adjustment knob and Fine adjustment knob.
- The Coarse adjustment knob is located at the right side of Microscope.
- The Fine adjustment knob is located at the left side of Microscope.
- coarse adjustment knob is used to focus the microscope. It is always used first, and it is used only with the low power objective.
- The fine adjustment knob is used to focus the microscope. It is used with the high power objective to bring the specimen into better focus
- Stage is a flat platform located below the objective lense, means between base and objective lens.
- Most of the microscope contains a mechanical stage, which has two knobs to control the slide.
- One knob moves the slide left and right, the other moves it forward and backward.
- The test specimen is placed over it for viewing.
7. Stage clips
- It is located over the stage.
- Each microscope contains two Stage clips.
- It holds the specimen slides in place.
- It is a hole in stage, which is located below the objective lense.
- Through Aperture the base (transmitted) light reaches the stage.
9. Microscopic illuminator
- Microscopic illuminator located at the base
Microscopic illuminators function as light sources for Microscope. it captures light from an external source of a low voltage of about 100v.
- A condenser may be defined as a series of lenses for illuminating with transmitted light an object to be studied on the stage of the microscope.
- Condenser is located under the stage next to the diaphragm of the microscope.
- They have a high magnification of 400X and above.
- Condensers with high magnification power can produce a high quality image.
Types of Condenser:
condenser used two methods of illumination;
A. Bright field illumination.
There are present Three Types of condenser which used in bright field illumination;
a. Abbe condenser
The Abbe condenser utilizes only two lenses. It is not corrected for spherical and chromatic aberration
b. Achromatic condenser
The achromatic condenser is corrected for both chromatic and spherical aberration.
c. Variable Focus Condensor
The variable focus condenser is a two lenses system in which the upper lens is fixed and the lower element focussable.
B. Darkfield illumination
There are present Three Types of condenser which are used in dark field illumination;
a. Abbe Condenser
It may be employed either by inserting a dark field stop below the condenser or by unscrewing the top part of condenser
b. Paraboloid Condenser
The paraboloid condenser is designed to be used with high power oil immersion objectives and an intense source of light
c. Cardioid Condenser
The cardioid condenser is specially designed to be used for the examination of colloidal solution or suspension.
- Condenser helps to collect and focus the light from the illuminator on to the specimen.
- It is located above the condenser and below the stage.
- Diaphragm also known as iris.
- High quality microscopes contain an Abbe condenser with an iris diaphragm. Combined, they control both the focus and quantity of light applied to the specimen.
- Diaphragm is used to vary the intensity and size of the cone of light that is projected upward into the slide.
12. Condenser focus knob
- It is located below the Condenser.
- It moves the condenser up or down thus controlling the focus of light on the specimen.
13. The rack stop
- It is located over the stage.
- It prevents users from moving the objective lenses too close to the slide, which could damage or destroy the slide and specimen.
- It is a type of Condenser with high resolution, approximately 400x or above.
- Abbe condenser is only found in high-quality microscopes.
- These types of condensers can produce a sharp or clear image with high resolution.