Parts of Microscope and Their Functions

By Sushmita Baniya •  Created: 05/09/22 •  6 min read

Microscope is a piece of laboratory optical equipment that is used to magnify small things that are too small for the details to be seen by the naked eye. The microscope is the microbiologist’s most basic tool, and every student of microbiology needs some background knowledge on parts of a microscope and how microscopes work.

The microscope was developed in the 16th century. Antony van Leeuwenhoek made the first modern microscope. He is also called the father of microscopy. Microscopy is defined as the use of or investigation with the microscope.

Do you know?
Antoni van Leeuwenhoek is the first person to see bacteria.

There are different types of microscopes based on their working mechanism and functions but the microscopes can be broadly classified into;

The Light Microscope  

Light microscopes are used to examine cells at relatively low magnifications. The limit of resolution of a light microscope is about 0.2 μm. This microscope uses visible light; shorter blue wavelengths provide better resolution.

Common light microscope used in the laboratory is called a compound microscope. It is so named because it uses two types of lenses; ocular and objective. Ocular lens is the Lens close to the eye and the objective lens is the lens close to the object. These lenses work together to magnify the image of an object. 

Parts of Compound Microscope      

Parts of Compound Microscope

Illuminator (Light Source)

As the source of light rays, a mirror or electric bulb is provided. The function of the mirror is to provide reflected light from a lamp or sunlight. Most microscopes, today have built-in lamps that provide necessary illumination.

You can turn on and off the light source using a switch and also adjust the intensity of light by turning the light adjustment knob. This knob is calibrated with a scale of 1 to 10; 1 is low intensity and 10 is high intensity.

Diaphragm (Irish)

Many microscopes have a rotating disk under the stage known as the diaphragm or iris. The diaphragm has different-sized holes that control the amount of light passing through it. Based on the transparency of the specimen, the diaphragm setting can be adjusted to achieve a needed degree of contrast.


Beneath the stage is a group of lenses that comprise the condenser. The condenser accepts parallel light rays produced by an illuminator and condenses them into a strong beam. It causes light rays from the light source to converge on the microscopic slide. Clarity of the image increases with the higher magnification of the condenser. Abbe condenser is present in the more sophisticated microscopes in which a higher magnification of 1000X is found. Condenser focus knob helps in the up-down movement of the condenser and aids in controlling the focus of light on the specimen. 


It is the hole present in the microscopic stage. Through the aperture, the transmitted light reaches the stage from the source.


Stage is a flat platform where we place the slides. It can also be moved up, or down with the aid of a sub-stage adjustment knob.  Stage clips are present in it that hold the specimen slides.

Objective lens

These are primary lenses that magnify the specimens. Four objective lenses are present in the compound light microscope. The shortest lens is the lowest power, the longest one is the lens with the greatest power. The higher power objective lenses are retractable, i.e. when they hit a slide, the end of the lens will push in thereby protecting the lens and the slide.

Objective lens of a microscope

Most ocular lens magnifies the image 10 times. So the total magnification of a microscope is calculated by multiplying the power of the objective lens by the power of the eyepiece (10x). For example, if you are observing an object by a scanning objective lens (4x), you are observing a 40 times magnified image (10x eyepiece lens multiplied by 4x scanning objective lens).

Body Tube

Transmits the image from the objective lens to the ocular lens. 

Ocular Lens (eye-piece)

Ocular lens of a microscope

Located at the top of the microscope, the ocular lens or eyepiece lens is used to look through the specimen. It re-magnifies the image formed by the objective lens usually by 10 times (10x) or 15 times (15x). Most microscope contains an eyepiece of 10x magnification power.

Eyepiece tube also known as the eyepiece holder holds the eyepiece lens together. They are flexible in the binocular microscope which can be rotated for maximum visualization. They are not flexible in the monocular microscopes.

Revolving Nose Piece

Several objective lenses of varying magnification are mounted on the revolving nosepiece. It is movable and the user can rotate it to achieve desired levels of magnification.

Coarse and Fine Adjustment Knob

Coarse Adjustment Knob

The coarse adjustment knob located in the arm of a microscope moves the stage up and down to bring the specimen into focus. The coarse adjustment is used to get the first focus. The gearing mechanism of the adjustment produces a large vertical movement of the stage with only a partial revolution of the knob. Because of this, the coarse adjustment should only be used with low power (4x and 10x objectives) and never with high power lenses (40x and 100x).

Coarse and fine adjustment knob of a microscope

Fine Adjustment Knob

Fine adjustment knob is generally found inside the coarse adjustment knob. It is used to bring the specimen into sharp focus under lower power and is used for all focusing when using a high power lens.


Arm of the microscope supports the tube and connects it with the base. Arm is used along with the base to carry the microscope. In the case of high-quality microscopes,  an articulated arm having more than one joint is present in it.


Base is the bottom of a microscope. It helps to support the microscope. Microscopic illuminator is also present in it.

References and further readings

Sushmita Baniya

Hello, I am Sushmita Baniya from Nepal. I am a postgraduate student of M.Sc Medical Microbiology. I am interested in Genetics and Molecular Biology.

Keep Reading

One response to “SEM vs. TEM Electron Microscopy”

  1. jaya suriya says:

    Tq sir the article was nice and informative almost useful in making my assignment.

We love to get your feedback. Share your queries or comments

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: