The term microscope first came from the Ancient Greek word μικρός, mikrós, means “small” and σκοπεῖν, skopeîn, means “to look” or “see“.

Microscope was first constructed in the 16th century, it was a revolutionary invention with its ability to magnify small objects such as microbial cells. It can produce high-resolution image of a tiny object with definitive structures which is not visible in naked eye.

Microscopes are laboratory instruments that are used to visualize very minute objects such as cells, microorganisms, giving a contrasting image, that is magnified. The microscope is made of a pair of lenses for magnification, each of these lenses contains their own magnification powers. Based on the types of lense it will enlarge the image of the specimen according to its focal strength.

These lenses are made of a special component that helps them to achieve high magnification levels. Microscope basically contains two sets of lenses which provides a much higher level of magnification, along with greater clarity. One lens is known as oculars, or eyepieces, and the second set of lenses are known as objectives.

A simple or compound microscope is made of two important parts such as the Structural parts and Optical parts. The structural parts provide supports to the microscope, while the optical parts help to produce a magnified image of specimens.

The structural parts of Microscope with their functions

This portion of microscope is made of three important parts such as Head, base and arm. Each of these parts has a unique role. 

1. Head: The upper portion of microscope known as head. The main function of this portion is, it holds the optical elements of the unit.
2. Base: The bottom portion of microscope is known as the base. The whole microscope stands on it.
3. Arms: This portion connects the head of the microscope to the base. It provides support to the head portion and also used to hold the microscope during carrying it. The modern microscope has an articulated arm that contains more than one joint which provides more movement of the head portion for better viewing.

The optical parts of Microscope with their functions

This portion of microscope helps to generate a high resolution or a magnified image of the specimen for better visualization. This portion is made up of different parts such as;

Parts of Microscope: 1) Eyepiece, 2) Nose piece, 3) Objective lens, 4) Stage clips or Slide holder, 5) Aperture, 6) Stage, 7) Adjustment knobs, 8) Stage controls, 9) Condenser lens, 10) illuminator

1. The Eyepiece Lens: It also termed ocular, located at the top of the microscope. It contains an ocular lens, user looks through it to see the magnified image of the specimen. The magnification power of ocular lens ranges from 5x to 30x, but 10x or 15x. The total magnifying power of Eyepiece can be calculated by multiplying with the magnification of the objective lens. For example, if the magnification power of an eyepiece is 10x and the magnification power of an objective lens is 40X then the total magnification power of the eyepiece will be 400X.
2. The Eyepiece tube: It holds the eyepiece and also connects the eyepiece with the objective lens. In a binocular microscope, the eyepiece tube is flexible, for that user can rotate the head for maximum visualization, at variance in distance. The monocular microscopes contain none flexible tube.
3. The Objective lenses: These are the main lenses, help for the visualization of the specimen. These lenses are closest to the object (specimen). A microscope usually contains 3 or 4 objective lenses, these are 4X (shortest lens), 10X, 40X, and 100X (longest lens). All high-quality microscopes contain achromatic, parcentered, parfocal lenses. Sometimes Abbe condenser is used to get the greatest clarity at high levels of magnification.
4. The Adjustment knobs: These knobs are used to focus the microscope on object. There are mainly two different types of adjustment knobs such as fine adjustment knobs and coarse adjustment knobs.
5. The Nose piece: Nose piece also termed revolving turret. It is a circular structure in which all the objective lenses are screwed in. It is used to change the magnification power, by simply rotate the turret.
6. The Stage: It is a flat platform, which supports the slides. The specimen placed over this section for viewing. It contains stage clips, which hold the specimen slides firmly in place. Some modern microscopes contain mechanical stage,  with adjustment knobs that allow for more precise positioning of slides. These mechanical stages contain two knobs, one knob shifts the slide left and right, the other moves it ahead and backward.
7. The Aperture: It is a hole on the microscope stage. The light transmitted through this hole from the source to the specimen.
8. Microscopic illuminator: This is basically a light source for a microscope, found at the base. It is a constant light source (110 volts in the US) that lights up through the slide. Sometimes microscopes use Mirrors, which are used to reflect light from an external light origin up through the bottom of the stage.
9. Condenser lens: This lens helps to focus the light from the source into the specimen and allows to produce sharp images at magnifications of 400X and above. It is located under the stage next to the diaphragm of the microscope. Some microscopes with 1000x power contain an Abbe condenser, it can be focused by pushing it up and down. During the 1000X magnification the abbe condenser should be set closest to the slide, as the magnification level gets lower it will move further away.
10. Diaphragm or Iris: It is located under the stage of a microscope and its main function is to regulate the amount of light that strikes the specimen. The diaphragm is a piece of adjustable apparatus, therefore regulating the light intensity and the size of the beam of light that gets to the specimen. In high-quality microscope, the diaphragm remains attached with an Abbe condenser, they are capable to regulate the light locus and light intensity that strikes the specimen.
11. The rack stop:  It regulates how distant the stages should go blocking the objective lens from hitting too close to the specimen slide which may destroy the specimen. It is effective for blocking the specimen slide from getting too far up and hit the objective lens.
12. Condenser focus knob: It controls the movement of the condenser up or down, therefore, controlling the focus of light on the specimen.
13. The Abbe Condenser: It is a type of high-quality condenser lens, design for use in high-quality microscopes. It is a movable condenser lens and can produce a very high magnification of above 400X. 

Parts of Different Microscopes

There are present different types of microscopes, which are classified based on their function such as;

1. Compound Microscope
2. Simple Microscope
3. Inverted Microscope
4. Dissecting Microscope or Stereo Microscope
5. Confocal Microscope
6. Fluorescence Microscope
7. Phase Contrast Microscope
8. Bright field Microscope
9. Dark field Microscope
10. SEM
11. TEM

Parts of a Compound Microscope

Parts of a Simple Microscope

Parts of a Inverted Microscope

Parts of a Dissecting Microscope or Stereo Microscope

Parts of a Confocal Microscope

Parts of a Fluorescence Microscope

Parts of a Phase Contrast Microscope

Parts of a Bright field Microscope

Parts of a Darkfield Microscope

Parts of a Transmission Electron Microscope

Parts of a Scanning Electron Microscope

MCQ on Parts of Microscope

References

1. Microbiology by Lansing M. Prescott (5th Edition)
2. https://www.amscope.com/microscope-parts-and-functions/
3. https://sciencing.com/parts-microscope-uses-7431114.html
4. https://www.microscopeworld.com/t-parts.aspx
5. https://www.microscope.com/compound-microscope-parts
6. https://www.microscopemaster.com/microscope-quiz.html