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Compound Microscopes

Modern science and technology scenario would not have been the same without the invention of microscopes. Let's learn the basics of the compound microscope.
Ningthoujam Sandhyarani Jan 27, 2019
You might have used microscopes in schools or colleges for viewing minute specimens like algae, fungi, virus, plant cell structures, animal cell structures, and other microorganisms. The study of fungi characteristics and their spores, microscopic algal forms, plant cells, and pathogens is possible only because of microscopes.
A microscope is an instrument used for viewing small objects that can't be seen with the naked eye. Microscope comes from the Greek word micros meaning "small" and skopeĆ®n  meaning "to look at".
There are three classes of microscopes, viz. light or the optical microscope, electron microscope, and scanning probe microscope. Among these, optical microscope is the most commonly used types. It uses visible light and a coordination of lenses magnify images.
Simple and compound microscopes are light microscopes. While a simple model involves usage of only one lens, a compound microscope uses more than one lens.
The invention of simple microscope is credited to Van Leeuwenhoek, the Father of Microbiology, who was the first to observe single-celled microorganisms. Later, Galileo Galilei, an Italian physicist, invented compound microscope in 1624 and named it "occhiolino" or "little eye".
In 1625, his fellow academy member Giovanni Faber coined the word "microscope" for Galileo's invention. It won't be wrong to say that the invention of compound microscope is a significant contribution to modern science.

Parts of a Compound Microscope

A compound microscope is named according to the fact that it uses a combination of lenses to magnify any sort of images. Basically, there are two components - the structural components and the optical components.

Structural Components

As the name suggests, these are the components that make up the configuration of a compound microscope. There are three basic structural components and they are as follows.
Head or Body - Head represents the upper part, and it consists the main optical parts.
Base - Base is the bottom part, which supports the microscope. The Illuminator is located in the base.
Arm - Arm supports the head component and connects it to the base.

While carrying a compound microscope, it is always recommended to handle the arm and support the base.

Optical Components

The working of a microscope entirely depends on the optical components. The optical parts are affixed to the rigid arm of the microscope.
Eyepiece - Eyepiece or oculars are secondary lenses located at the top, near the eye. It is through this lens that we view an object in a microscope. Mostly, their magnification is 10x.
Objectives - Objectives are the primary lenses of a compound microscope. Typically, there are 3 - 5 objective lenses of different powers. Their magnifications range from 4x - 100x.
Nosepiece - Nosepiece supports the objectives. The objectives are mounted on a rotating turret so that any of the objectives can be conveniently used for viewing.
Coarse and Fine Adjustment Knobs - Coarse and fine adjustment knobs are used for focusing, so as to get a clear image of the object.
Stage - Stage is the platform, where the slide to be viewed is placed. For higher magnification studies, mechanical stage is used for fine movement of the slide.
Stage Clips - Stage clips are used to keep the slide in place, where there is no mechanical stage.
Diaphragm - Diaphragm is a rotating disc located below the stage. It is used to control the amount of light reaching to the specimen.
Condenser - Condenser collects light from the illuminator and focuses it onto the object. It is located below the stage and in association with the diaphragm.
Body Tube - Body tube or eyepiece tube is the part that connects the oculars to the objectives. Thus, oculars are placed at the upper portion above the objectives.
Aperture - The hole in the stage is aperture. It is through this hole that transmitted light reaches the object.
Illuminator - Illuminator is the source of light in a microscope. It is placed in the base component.

Working of a Compound Microscope

The setup of the optical parts plays an important role in working of a compound microscope. The condenser after collecting light from the illuminator focuses the light onto the specimen. The objective lens, which is of very short focal length, forms a highly magnified, inverted image of the specimen.
The enlarged image is passed to the projector lens that reverses the direction so that the final image is an erect one. Then from the projector lens, light rays travel to the eyepiece, which again magnifies the image with respect to its magnification power. Thus, final image is created and projected to the eye.
The magnification of a microscope is calculated by multiplying the eyepiece magnification power and the objective magnification power. For example, if the eyepiece power is 10x and objective power is 40x, then the resulting magnification is 400x.

Handling a Compound Microscope

A microscope is a delicate instrument, so proper care must be taken while handling it. Following are some instructions, which will be helpful while handling or transporting it.
Carefully read and follow the instructions given with instrument while using microscopes.
Always handle by the microscope arm with one hand and support the base with the other hand.
Avoid touching lens surfaces with your hand as even a minute particle of dust from your hand can cause scratches. While cleaning lenses, used proper lens cleaner and paper. Use damp cloth to clean the other parts.
Cover your microscope properly when not in use. This will protect from other things to come in contact with the lens surfaces.
Periodically, it should be serviced by a professional technician.
Nowadays, compound microscopes are used in various domains, within or outside science. By understanding these basics, you can independently carry out an experiment for observing minute objects of your interest, and explore some of the incredible things. You can always seek the help of an expert while buying a microscope.