Compound Microscope Drawing With Parts and Functions

In this compound microscope drawing with parts and functions post we have briefly explained about compound microscope, principle, compound microscope objective lens, other parts, functions, applications, and uses.

Compound Microscope

The microscope is an extremely useful tool. There are many small objects or details of objects which cannot be seen by the unaided human eye. The microscope magnifies the image of such objects thus making them visible to the human eye. Microscopes are used to look at the form of bacteria, fungus, parasites, and host cells in different colored and unstained preparations.


In microbiology, the compound light microscope is the most commonly used microscope. To magnify the image, it has two lens systems (compound microscope objective lens system). The magnification power of compound microscope objective lens varies. Monocular refers to a compound light microscope with a single eyepiece; binocular refers to a complex light microscope with two eyepieces.

Compound microscope objective lens (usually 4X, 10X, 40X, or 100X) in a rotating nosepiece closer to the specimen, and the eyepiece lens (commonly 10X) in the binocular eyepieces, make up a compound microscope.

In today’s world, a compound binocular microscope is more widely utilised. Bright field microscopes are commonly known as compound microscopes. Upright and inverted compound microscopes are two types of compound microscopes.

Upright compound microscopes are similar to traditional microscopes in that they have a lens system, a stage where the specimen is maintained, and a light source.

Inverted compound microscopes are a mirror image of upright compound microscopes, with the illumination system coming first, then the stage, and finally the lens system.

Compound Microscope Principle

Compound Microscope Drawing With Parts and Functions


Compound microscope are works on the principle that when a tiny specimen to be magnified is placed just beyond the focus of its compound microscope objective lens, a virtual, inverted, and highly magnified image of the object is formed at the shortest distance of distinct vision from the eye held close to the eyepiece.


1. Light Microscope

Bright-field Microscope

Dark-Field Microscope.

Phase-contrast Microscope.

Fluorescent Microscope.

2. Electron Microscope

Scanning Microscope

Transmission Microscope

Confocal Microscope

Working Mechanism

The specimen or object to be examined is typically mounted on a clear glass slide and placed on the specimen stage between the condenser and compound microscope objective lens. A condenser lens focuses a beam of visible light from the base onto the specimen.

Compound microscope objective lens collects the light transmitted by the specimen and magnifies it to create the primary image inside the body tube. The ocular lens or eyepiece magnifies this image once more.

When a higher magnification is required, the nose piece is rotated after low power focusing to align the objective of a higher power (typically 45X) with the illuminated portion of the slide.

It was occasionally necessary to use a magnifying glass with a very high magnification (e.g. for observing bacterial cell). In such cases, an oil immersion compound microscope objective lens (typically 100X) is used.

Because the image is produced in a brightly illuminated field, the common light microscope is also known as a bright-field microscope. Because the specimen or object is denser and more opaque than its surroundings, the image appears darker. A portion of the light passing through or through the object is absorbed.

Magnification Power

The total magnification of image formed by the compound microscopes is calculated b this following formula;

M    = D/ fo * L/fe   

Where,   D = Least distance of distinct vision (25 cm)

              L = Length of the microscope tube

              fo = Focal length of the objective lens

              fe = Focal length of the eye-piece lens


Eye piece

Through the eyepiece, the specimen is observed. It is equipped with a lens that enlarges the image created by the objective. The eye-magnification piece’s ranges from 5X to 20X.

On the inside of the eyepiece, a movable pointer can be attached. The two eyepieces in a binocular microscope can be adjusted closer or farther apart to accommodate for the distance between the eyes using a pulling pushing motion or a knurled ring.

Microscope tube

The arm has a microscope tube connected to it. It might be monocular or binocular in nature. On the higher end, it supports the eyepiece.

Mechanical tube

The mechanical tube length is the distance between the objective and the top of the draw-tube, where the eyepieces are inserted.

It is not tubular in current microscopes; instead, prisms bend the light coming up, offering a suitable viewing angle. The light is split and supplied to both eyepieces through a binocular tube.

Nose piece

The nosepiece is linked to the microscope tube’s arm. The goals are housed in the nose-piece, which rotates them. The objectives are arranged in order of increasing magnification power, from lowest to highest. This keeps the immersion oil from contaminating the intermediate targets.

Compound Microscope Drawing With Parts and Functions


The image of the specimen first passes through the objective. Objectives with magnifying powers 4X, 10X, 40X and 100X are commonly used. The magnifying power is marked on the lens and is usually colour-coded for easy identification.

Mechanical stage

The mechanical stage holds the slide and allows it to be moved to the left, right, forward or backward by rotating the knobs. It is fitted with fine vernier graduations as on a ruler. This helps in relocating a specific field of examination.


The condenser illuminates the specimen and controls the amount of light and contrast. There are different types of condensers. Some condensers have a rack-and pinion mechanism for up-and-down adjustment.

Two sided mirror

A mirror is the simplest illuminator. The two-sided mirror provides necessary illumination through reflection of natural or artificial light.

It has two surfaces, one plain for artificial light and other concave for natural light. It is supported on two sides by a fork fixed on a mount in a way that permits free rotation.

Immersion oil

Immersion oil must be used with objectives having NA more than 1.0. This increases the resolving power of the objective. 

An immersion oil of medium viscosity and refractive index of 1.5 is adequate. Any synthetic non-drying oil with a refractive index of 1.5 and/or as recommended by the manufacturer should be used.

Coarse Focusing Knobs

The coarse focusing knob alters this distance rapidly and is used to bring the specimen into the field of view using an objective having low magnification power.

Fine Focusing Knob

The fine focusing knob changes the distance very slowly and permits better viewing of the object. One revolution of the fine focusing knob should generally move the mechanical stage by 100 µm. The movement should be smooth and free from jerks.


  1. In pathology labs, a compound microscope is very useful for identifying diseases and blood analysis.
  2. Compound microscopes are employed in forensic laboratories to examine human cells, paper, and other items related to a crime scene.
  3. Compound microscopes can detect the presence or absence of minerals, as well as the presence or lack of metals.
  4. Drugs are detected by looking at their particles under compound microscopes.
  5. Compound microscopes are used in university and college laboratories to examine fungi, bacteria, plant cells, animal cells, and other organisms.
  6. It allows you to observe and understand the microbiological world of bacteria and viruses, which is otherwise hidden from view.
  7. A compound microscope is used to examine plant cells and determine the bacteria that thrive on them. A compound microscope has therefore proven to be essential for biologists.

Further Readings