Compound Microscopes

You might be quite aware about using microscopes in schools, colleges and other research laboratories for viewing minute specimens like algae, fungi, viruses, plant cell structures, animal cell structures and other microorganisms. The study of fungal characteristics and their spores is possible only because of microscopes. In fact, have there been no microscopes, there would not have been microbiology subject as such.

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 skopeîn meaning "to look at". In general, there are three classes of microscopes viz. light or optical microscope, electron microscope and scanning probe microscope. Among these, optical microscope is most commonly used. It is a type that makes use of visible light and a coordination of lenses to magnify images. Simple and compound microscope are light microscopes. Simple microscope uses only one lens, whereas 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. In fact, the invention of compound microscope is a significant contribution to modern science.

Parts of a Compound Microscope

A compound microscope is so called because it uses a combination of lenses to magnify any sort of images. Basically, there are two components - the structural components and the optical components. Let's see in brief about the components and their parts in a compound microscope.

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 of a compound microscope.

Base - Base is the bottom part, which supports the microscope. Illuminator is located in the base.

Arm - Arm supports the head component and connects it to the base.

It is always recommended to handle by the arm and support the base while carrying a compound microscope.

Optical Components

Working of a microscope entirely depends on the optical components. The optical components 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 in a compound microscope. Their magnifications ranges from 4x-100x and are leveled on their sides.

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 effect.

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. In this, 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 objective magnification power. For example, if the eyepiece power is 10x and objective power is 40x, then the resultant magnification is 400x.

Handling a Compound Microscope

A microscope is a delicate instrument, so care must be taken while handling it. Following are some instructions, which would be helpful while handling or transporting it.

• Read and follow the instructions given with instrument carefully 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.

By understanding these basics, you can independently experiment to observe any minute objects of your interest and try to explore some of the incredible things with the help of this wonderful instrument. Nowadays, compound microscopes are used in various domains, within or outside science. Care should be taken while buying any of the microscopes, be it compound or digital microscope. For better understanding, you can always discuss with a science teacher or an expert.