Parts of a Compound Microscope

What is a Compound Microscope? 

A compound microscope is a type of microscope that uses two sets of lenses to magnify the image under the microscope. It has an objective lens that has a resolution of 4x,10x, 40x, 100x, and an eyepiece of resolution of 10x. The usage of both lenses, compounds or magnifies the image of the object below the objective lens to achieve a resolution of 40x, 100x, 400x, 1000x.

Parts of a Compound Microscope

  1. Mechanical Parts

  2. Optical Parts

Mechanical Parts:

  • Base (Foot): It is the base at which the microscope stands on. It is a U-shaped structure.

  •  Pillar: It is the stand that lies on the stage and is a perpendicular projection.

  • Arm: The whole microscope is managed or carried by the curve-shaped structure called the arm.

  • Stage: It is the rectangular structure that has a hole in the center that allows the light to pass through it. It is below the eyepiece, and most of the specimens are placed on this stage to examine.

  • Inclination Joint: It is the point where the pillar meets the arm. The whole microscope can tilt at this inclination joint.

  • Clips: The stage, on the side of the specimen holder, contains clips that hold the slides on which samples will be placed.

  • Diaphragm: It is a structure located below the stage which controls the intensity of light entering the stage. It is of two types: disc and iris.

  • Nose piece: The body tube has three holes that have places to fit the objective lens. This structure is called the nose piece.

  • Body tube: It is the hollow tube at the upper arm, which has one end of the eyepiece lens, and another term has an objective lens. The body tube is altered using the adjustment knobs.

  • Fine adjustment knob: It is a tiny knob that is used for focusing on the slide accurately. This knob can make only small adjustments.

  • Coarse adjustment knob: It is a comparatively bigger knob that is used for more significant alterations.

Optical Parts:

  • Eyepiece: It is the lens used on the upper part of the body tube. It usually has a resolution of 10x but can be of 5x or 15x. It is the lens through which the person views the specimens.

  • Objective lens: It is the lens used on the lower part of the body tube. It is attached to the nose piece. Usually, three or four nose pieces are available, which contains the objective lens of different resolutions like 10x, 40x, 100x.

  • Mirror: A concave mirror on one side and plain mirror, on the other hand, can be seen below the stage to focus the light on the stage for a brighter image of the specimen.

 The Working Mechanism of a Compound Microscope

  1. The person using the lens must first arrange the eyepiece. They must arrange the mirror in a manner that the maximum amount of light reaches at the end of the stage. This ensures that the specimen has adequate light for viewing. 

  2. The dust on the lenses, mirror, and stage is cleaned so that a clear image of the specimen can be seen.

  3. The slide that is to be examined should be placed on the stage, and clips are put so that the slide does not move.

  4. The nose piece is adjusted below the object to be focused.

  5. When the person views through the eyepiece, the light from the mirror below the stage reflects the object of focus. 

  6. This light travels to the objective lens and the eyepiece to the eye of the person.

  7. A more unobstructed view of the specimen is obtained when the coarse adjustment knob in the microscope is used. The fine adjustment knob gives an accurate picture of the sample.

  8. The primary principle used here is the principle of compounding or magnification. The magnification factor of the eyepiece multiplied with that of the objective lens. This principle produces a magnified image.

  9. First, the specimen must be focused under the low-resolution objective lens by coarse adjustment. Any necessary diagrams can be drawn by viewing from this resolution.

  10. If you want more resolution on the same specimen, the nose piece is turned into a higher resolution. At this point, only a fine adjustment knob should be used as a coarse adjustment knob can crush the slide.

  11. The resolution of the eyepiece remains constant, but the resolution of the objective lens can be changed by rotating the nose piece. Hence, the same microscope can be used to view the object of focus in different magnifications.

  12. The person viewing the microscope should place the lens in a well-lit place so that an adequate amount of light strikes the concave part of the mirror under the stage.

  13. Diagrams can be drawn once a proper image of the specimen is seen under the microscope.


  1. The microscope should be lifted with the help of both arms and base together.

  2. The eyepiece and objective lens must be cleaned by silk cotton and transparent liquid, so that dust accumulated on the lens does not hinder the viewing of slide or focus.

  3. The microscope must not be disturbed by tilting or shaking it while using it. This bouncing alters the light received by the lens, and the viewing of the object of focus alters.

  4. Always the specimen must be first focused under the low-resolution lens, then later high-resolution lens must be used to target it furthermore.

  5. After you complete using the compound microscope, the objective lens of the lower power must be focused on the stage. 

  6. When a person is using the coarse adjustment lens, care should be taken that the objective lens does not touch the slide of focus. Sometimes, the coarse adjustment lens, when used rapidly, may crush the specimen to be observed, and precise results cannot be obtained, and  the example and the slide also may be damaged.

  7. If you are using a high-resolution lens for a specimen, the fine adjustment knob should only be employed. Do not use the coarse adjustment knob as it cannot give accurate results for viewing smaller details.

  8. Always use a coverslip on the slide of the specimen. This ensures other particles do not accumulate on the sample and alter the results.

  9. If you are using an oil immersion lens, the oil should always be used for accurate results. As without the use of oil, the refractive index may be changed, which manipulates the reading of the specimen.

  10. Always place the microscope inside a box after completion.

  11. The mirror has a concave part that is used in dim light to get a better view.  

  12. The microscope must not be dismantled.

  13. Always use a clean slide or clean the slide with proper water and wipe it so that any stains on the slide do not appear under the microscope. This can confuse the person whether the perceived object is a stain or a part of the specimen.