Compound Microscope

As the name suggests, a compound microscope uses a combination of lenses coupled with an artificial light source to magnify an object at various zoom levels to study the object.

A compound microscope:

• Is used to view samples that are not visible to the naked eye
• Uses two types of lenses – Objective and ocular lenses
• Has a higher level of magnification – Typically up to 2000x
• Is used in hospitals and forensic labs by scientists, biologists and researchers to study microorganisms

Invented in the late 16th century by Zacharias Janssen, compound microscopes have contributed immensely to the medical field.

It has helped scientists, researchers and doctors in studying the microorganisms, their cells and DNA.

This understanding of the microorganisms has helped scientists in studying how different conditions and diseases attack various cells in our body and several medical advances have been possible, thanks to the compound microscope.

What actually is a Compound microscope?

• Also called as binocular microscope or compound light microscope, it is a remarkable magnification tool that employs a combination of lenses to magnify the image of a sample that is not visible to the naked eye.
• Compound microscopes find most use in cases where the magnification required is of the higher order (40 – 1000x).
• The magnification effect is achieved using the combination of the objective lens (near the sample) and the ocular lens (within the eyepiece).
• The final magnification achieved by the microscope is measured by multiplying both the magnification achieved by objective lens and the magnification achieved by ocular/eyepiece lens.

Working principle

Using a combination of lenses, the working principle of a compound microscope is that a highly magnified image of the specimen is formed at the least possible distance from the distinct vision of an eye that is held very close to the eyepiece of the microscope when the specimen is placed just beyond the focus of the objective lens.

The magnified image is always an inverted and virtual image of the specimen.

Compound Microscope Parts (Labeled diagram)

A compound microscope basically consists of optical and structural components. Within these two systems, there are multiple components within them and they are:

 

Image : Labeled Diagram of compound microscope parts

See: Labeled Diagram showing differences between compound and simple microscope parts

Structural Components

The three structural components include

1. Head

This is the upper part of the microscope that houses the optical parts

2. Arm 

This part connects the head with the base and provides stability to the microscope. Arm is used to carry the microscope around

3. Base 

Base is on which the microscope rests and the base houses the illuminator that lights up the specimens.

Optical Components

Objective lenses and Eyepiece lenses are the two major optical systems in a compound microscope. The various optical components include:

4. Eyepiece Tube

The tube aids in keeping the eyepieces in their place above the objective lens. These binocular microscopes typically have a diopter adjustment ring that is used to adjust for the variations in our eyesight in one or both eyes.

5. Aperture

The stage has a hole through which the transmitted light from the base falls on the stage to illuminate the slide. This hole is called the aperture.

6 (a,b). Fine and Coarse Focus knobs

These knobs are used to adjust the focus of the microscope. In the recent past, these two knobs are coaxial housed to offer convenience to the user. Usually, both the knobs are built on one axis with the fine focus knob placed on the outside to enable the users to fine tune the focus.

7. Eyepiece

The eyepiece is at the top of the microscope and it is through this we see the specimen. Eyepieces usually have a magnifying power of 10x and the magnifying power can be increased or decrease depending on the usage by interchanging the lenses.

8. Nosepiece

This is the part that hosts the objective lenses. The objective lenses are mounted on a rotating turret and different lenses can be selected and exposed depending on the user’s requirement.

9. Stage Clips

These clips are used when there is no mechanical stage. The user needs to manually move the slide containing the specimen to view the various sections within the sample.

10. Objective Lens

The most important optical component on the microscope, objective lens can have a magnifying power ranging from 4x to 100x. A combination of about 4 – 5 lenses are used on microscopes depending on the required magnifying power.

Depending on the level of complexity of the specimen, the magnifying power is chosen and accordingly the lenses are used. These objective lenses can be either rear-facing or forward-facing.

11. Iris Diaphragm

It regulates the amount of light reaching the specimen that needs to be viewed under the microscope. It is located under the stage and over the condenser. Modern day microscopes use a combination of condenser and iris diaphragm to control the quantity of light and focus being applied to the specimen.

12. Stage

The specimen that is to be viewed is placed on the stage. Depending on the requirement of working at higher magnifications, a mechanical stage is used to enable the delicate movements that may be required with the specimen.

13. Condenser

It collects and focuses the light from the illuminator onto the specimen. It is housed under the stage and is often used in combination with the iris diaphragm.

14. Illuminator

This is the light source for the microscope and is usually located in the base of the microscope. The modern day microscopes use halogen bulbs operating at low voltage and have the capability to operate at variable lighting settings to facilitate convenience for users.

For instance, the users can increase or decrease the intensity of light being focused on the specimen being viewed. The lighting control is incorporated in the base of the microscope.

15. Condenser Focus Knob

This knob is used to control the movement of the condenser in the process of controlling the light focus on the specimen

16. The Rack stop

This component regulates the movement of the stage lest the specimen gets in contact with the lens thereby increasing the chances of damaging the specimen.

For in-detail information on: Parts of Compound microscope

Frequently asked Questions

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