Objective

To study the parts of a compound microscope.

Theory

Compound microscope

A compound microscope is a high-resolution, multi-lens device used to view and magnify objects not visible to the human eye. It uses two sets of lenses providing a 2-dimensional image of the sample.

Objective lens – The primary lens has a magnification capacity of 4X, 10X, 40X, or 100X, is positioned close to the object, and forms an inverted image with apparent magnification.
Eyepiece or Ocular lens – The secondary lens or ocular lens is at the top to view the observed image.

Parts of a compound microscope

The parts of a compound microscope can be categorized into:

Mechanical components - Including head, eyepiece tube, arm, stage, stage clips, nosepiece, condenser, focus knobs (coarse and fine adjustments), and base.
Illumination Components - Including illuminator.
Optical components - Including eyepiece (ocular lens), objective lens, diaphragm.

Mechanical components

Head and eyepiece tube: The upper part of the head attached to the eyepiece tube supports optical components, maintains lens alignment, and supports the eyepiece tube for optimal performance.

Base and arm: The base and arm of the microscope provide stability and facilitate the connection of the base and upper parts, ensuring easy handling and transportation.

Stage and clips: The stage is a flat platform attached to the arm with an adjustable height. The clips help to hold the slides, and the center hole passes the light to the object.

Condenser: It is located under the stage and is positioned between the stage and the diaphragm. It regulates the light intensity that passes from the illuminator to the hole.

Nosepiece: It is a circular; rotating metal part positioned at the bottom of the body and holds three different objective lenses.

Focusing knobs (coarse and fine adjustments): The coarse adjustment knob adjusts for general focus by moving the body tube up whereas the fine adjustment is used for clear visualization.

Optical components

Eyepiece (ocular lens): The eyepiece at the top of the body tube visualizes the magnified image by objective lenses to the closest view.

Objective lens: It is located at the top of the stage, magnifies and projects the magnified image of the specimen which can be observed through the eyepiece.

Oil immersion objective (100X) - Ideal for maximum magnification to observe fine details, and enhance resolution, and clarity of the structure of bacteria or cellular components.
High power objective (45X) - Ideal for detailed examination of specific specimen features after initial scanning.
Low power objective (10X) – Ideal for initial observation and location, also offering a wide field view and frequent scanning of the entire specimen.

Diaphragm: The diaphragm, located below the stage controls the amount of light reaching the specimen. It is of two types: disc and iris.

Illumination components

Illuminator: It is the light source, either a mirror or light used to illuminate the object to the eyepiece.

Significance of compound microscope

Magnification power allows to magnify the image clearly for a comprehensive analysis of the sample, yielding detailed information.
User-friendly and easy to operate.
Versatile application plays a major role in biology, medicine, and all material sciences for detailed study.
Research assistance supports the study of new discoveries, providing enhanced visualization and strengthening research efforts.

Limitations of compound microscope

Limited resolution: It has the limited capacity to display extremely fine details, particularly when using very high magnification.
Sample preparation: Prior to examining under a compound microscope, many specimens require special preparation.
Potential damage to specimens: Delicate specimens can be harmed if not handled carefully while being prepared for viewing under a compound microscope.

Uses of compound microscope

Useful for learning about microorganisms and their functions, including cell division and cellular processes.
Assists in analyzing studies of leaves, stems, roots, and reproductive organs to learn plant anatomy and physiology.
Facilitates to understanding the structure of microorganisms using permanent slides and samples obtained from the environment.

Precautions 

Eyepieces must be cleaned using a silk cloth and cleaning liquid before use. 
Avoid tilting while working or using the microscope.
Start focusing the specimen from the lower magnification and then to the higher. 
Avoid objective lenses hitting the stage while focusing.
For well–mount preparation, a coverslip must be used before observing. 
Ensure the immersion oil is applied before focusing on higher magnification.

Learning outcomes

Student understands,

The concept of compound microscope.
The various parts and working mechanism of the compound microscope.
The significance, limitations, and uses of the compound microscope.