How to Use a Compound Microscope: 12 Steps

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How to Use a Compound Microscope: 12 Steps
How to Use a Compound Microscope: 12 Steps

A compound microscope is a powerful magnifying tool used in scientific laboratories to observe bacteria or other organisms in the same range. These microscopes require at least two convex lenses positioned on opposite sides of a tube. As the top of the tube, the eyepiece, is raised or lowered, the image at the other end is in focus and magnified. Despite its complex nature, you don't have to be a scientist to learn how to use one.


Part 1 of 2: Understanding the Microscope

Use a Compound Microscope Step 1
Use a Compound Microscope Step 1

Step 1. Familiarize yourself with the microscope

Examine all the parts and learn their names and functions. If you are in class, the teacher should go over this information with the students. If you are trying to learn on your own, you may have received a diagram with this information along with the microscope.

  • The microscope should be placed on a clean, level surface, near an electrical outlet.
  • Always carry the microscope with both hands. Support the arm or spine with one hand and the base (also called the foot) with the other.
Use a Compound Microscope Step 2
Use a Compound Microscope Step 2

Step 2. Turn on the microscope

To do this, you will have to connect it to a suitable outlet. The power button is usually located on the base of the microscope.

  • Electricity is necessary for the illumination components of the microscope.
  • Make sure the source of electricity is the most suitable for the microscope. Usually these microscopes require a 120 volt power supply.
Use a Compound Microscope Step 3
Use a Compound Microscope Step 3

Step 3. Check the optical system

This holds the optical components, which include the eyepiece, tube, nosepiece, and objective lenses. This part is also known as the body of the microscope.

  • The eyepiece is what allows you to see the sample under the microscope.
  • The tube holds the eyepiece.
  • The revolver holds the objective lenses.
  • Objective lenses are the most important in the compound microscope. Depending on their complexity, they can be 3, 4 or 5.
Use a Compound Microscope Step 4
Use a Compound Microscope Step 4

Step 4. Study the arm

This connects the optical system to the base or foot. There is no lens in this part.

  • When you carry a microscope like this, be sure to hold it by both the arm and the base.
  • The arm supports the optical system.
Use a Compound Microscope Step 5
Use a Compound Microscope Step 5

Step 5. Examine the base

This provides a foundation for the microscope and is where the samples are placed. The base also has the focus knobs (the fine and the rough).

  • Knobs or screws can be separate or coaxial (meaning both settings are on the same axis).
  • The stage is the place where the sample or specimen is placed. When a higher magnification is required, a mechanical stage can be used.
  • The clamps are used to make manual adjustments to the stage.
Use a Compound Microscope Step 6
Use a Compound Microscope Step 6

Step 6. Learn about lighting

These microscopes include an illumination system that improves visualization. These light sources are located at the base of the device.

  • Light enters the stage through a hole through which the light reaches the sample.
  • Illumination provides the light to the microscope. Low wattage bulbs are generally used. The light is continuous and variable.
  • A condenser receives the light and focuses it. It is located under the stage and is usually attached to the diaphragm or iris.
  • The condenser focus knobs move it up and down to adjust the light input.
  • The diaphragm is located under the platen. Together with the condenser, it is in charge of controlling the focus and the amount of light that the specimen receives.

Part 2 of 2: Focusing the Microscope

Use a Compound Microscope Step 7
Use a Compound Microscope Step 7

Step 1. Prepare the sample

You should always have a glass coverslip over the specimen you want to see under the microscope. This also serves to protect the microscope lens in case it comes into contact with any sample.

  • Place the specimen between a slide and a coverslip to create the specimen.
  • Place the sample in the center of the stage, over the opening.
  • Make the sample fit between the tweezers to hold it.
Use a Compound Microscope Step 8
Use a Compound Microscope Step 8

Step 2. Make sure the diaphragm is open

This is located under the platen. The idea is that as much light as possible reaches the sample and the lens.

  • The iris should not be used to control the amount of light, but to optimize the level of contrast and resolution in order to see everything more clearly.
  • Usually used at the lowest magnification level.
Use a Compound Microscope Step 9
Use a Compound Microscope Step 9

Step 3. Arrange the revolver and knobs

Start from the lowest level of magnification. In this way, you will be able to select the part of the specimen that interests you the most. Once you locate it, you can start increasing the magnification level to get a better view of the given area.

  • Rotate the revolver until the shorter objective lens (4x) is on the specimen. Once it snaps into place, it will sound and feel stiffer. The shortest lens is the least powerful and the easiest to use when first starting to observe samples.
  • Turn the coarse (coarse) or coarse focus knob on the side of the base so that the stage is closer to the short lens. Make sure to do it without looking through the eyepiece. Also remember that it is important that the sample does not touch the lens. Stop adjusting the knob just before the glass touches the lens.
Use a Compound Microscope Step 10
Use a Compound Microscope Step 10

Step 4. Focus the microscope

Looking through the eyepiece, adjust the light source and aperture to achieve the proper light level. Move the slide so that the specimen is in the center of the lens.

  • Adjust the light until you are comfortable with the amount. The more light there is, the better you can see the specimen.
  • Turn the coarse knob to the opposite side so that the stage is away from the lens. Do this slowly until you can better focus on the sample.
Use a Compound Microscope Step 11
Use a Compound Microscope Step 11

Step 5. Increase the size of the image

Use the coarse knob to place the sample in the desired location and the fine knob to readjust. The slide may need to be accommodated as you use the magnification.

  • When using a compound microscope, the correct way to observe is to keep both eyes open. One should look through the eyepiece and the other outside the microscope.
  • When using the 10x magnification lens, it is a good idea to lower the light intensity to see more clearly.
  • Readjust the light source and aperture as necessary.
  • Change to a longer objective lens by rotating the revolver.
  • Adjust the focus as necessary.
  • Once the image is clear, switch to a higher magnification lens. This process is easier and you will only have to adjust the focus a little.
  • If you cannot focus the sample, repeat the steps above.
Use a Compound Microscope Step 12
Use a Compound Microscope Step 12

Step 6. Put the microscope away

Dust can damage the compound microscope as it can damage the lenses, jam the knobs, and affect the quality of the image you see through the eyepiece.

  • Always turn off the microscope when you are done using it.
  • Lower the stage, remove the sample, and cover the equipment with a dust-free cover.
  • Avoid touching the lenses or any piece of glass with your fingers.
  • Always carry the microscope carefully and with both hands.


  • Since the specimen is viewed through multiple lenses, it is an upside-down image. Therefore, you will need to bring the sample closer to the objective lens in order to see it further through the eyepiece.
  • Deposit less than the required amount of specimen between the slide and the coverslip so that the contents are spread sideways.
  • Make sure the microscope has a limit to the movement of the stage. Otherwise, you will have to be very careful when moving it in such a way that the lens does not come into contact with the glass, as it could break.


  • Do not place the microscope on a surface that is not level, as you will not be able to focus properly and the microscope could wobble and fall.
  • Always carry the microscope with both hands. One hand should support the arm and the other the base. Remember that it is a fragile and expensive device.
  • Do not touch the glass components with your fingers. This can damage the lens and render it useless.
  • Keep both eyes open when using the eyepiece. While you only use one eye to see the sample, you could strain your eyes too much if you keep the other closed.

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