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Parts of A Compound Microscope – A Definitive Guide

To be able to correctly use a compound microscope, it is important to know all its different parts and how each one works. Otherwise, you might not be able to properly view the specimen you are studying, or worse, risk breaking or damaging the microscope due to improper use.

We will go in great detail on each individual part of a compound microscope, but here is a brief run down, if you want the short answer to the question,

What are the parts of a compound microscope?

The microscope head consists of the eyepiece and the revolving nosepiece where the objective lenses are, and these two are connected via the eyepiece tube. The main body of the microscope houses the coarse and fine adjustment knobs, as well as the specimen stage. Finally, the base is where the light source and power switch are located.

Read on further to find out more detail as to what each part of the microscope is for and how it works, and learn more about common questions when it comes to compound microscopes, including the steps on using one.

Compound Microscope: Frequently Asked Questions

Before we delve deeper into the many different parts of a compound microscope, let us first understand things a little better by talking about just what a compound microscope is, how it works, and what it’s used for.

Below are three of the most common questions surrounding compound microscopes. If you want a more in-depth guide, you may check out our article on everything you need to know about a compound light microscope.

What is a compound microscope?

Microscopes are scientific devices that are used to magnify an object in order to see its minute details. In this case, a compound microscope is a type of microscope that is used for very small specimen samples to study its features that are otherwise not visible to the naked eye.

As compared to other types of light microscopes such as stereo microscopes and low power microscopes, a compound light microscope can achieve higher levels of magnification, generally up to 1000x, and sometimes even up to 2000x.

How does a compound microscope work?

A compound microscope uses a compound lens system. This means that the microscope has two lenses, where the objective lens magnifies the specimen, and the ocular lens on the eyepiece further magnifies the image from the objective lens. These two optical systems are what make compound microscopes have a high level of magnification.

Light from the illuminator is collected by the iris diaphragm and focused by the condenser. It passes through the aperture and through the specimen on the stage, then further on through the objective lens which magnifies the image, then this image travels through the eyepiece tube, and finally, gets further magnified through the eyepiece.

What is a compound microscope used for?

Due to its high magnification power, a compound microscope is a suitable imaging device for viewing and studying smaller specimens such as cells, cell structures, and tissues of plants, animals, and microorganisms.

It is an inexpensive yet invaluable tool for students and scientists alike who are engaged in various scientific fields such as biology, chemistry, bacteriology, and even forensics. You can find a compound microscope in most science classrooms, laboratories, and medical facilities.

The Parts of a Compound Microscope

Compound Microscope parts
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Compound light microscopes are more complicated than a simple microscope, a.k.a. a microscope with one lens, which was first invented in the 17th century. Hence, they have more parts, and therefore require several steps to use.

These parts can be classified into two general categories, which are optical components such as the objective lens and the ocular lens, and structural components like the illuminator, stage, and adjustment knobs.

Essentially, a compound microscope has three sections- the head, body, and base. Each of these sections consist of many different parts, each with their own specific purpose. Below are the different parts of a compound microscope, arranged according to where they can be found on the microscope:

The head

The microscope’s head is its uppermost section. It’s a fixed and immovable part of the microscope that holds a couple of important parts, more specifically, the optical systems of the microscope.

This is where the eyepiece is located, or the lens that you use to look at the specimen beneath. This eyepiece extends from the eyepiece tube, and can be controlled through the diopter adjustment. Moreover, the head also houses the revolving nosepiece, which is where the objective lenses can be found.

Here are the different parts you can find on the head:

Eyepiece

As the name suggests, the eyepiece is the viewing area of the microscope. It’s where you look to see the magnified image of the specimen you are analyzing. The eyepiece is also called the ocular lens, since it’s a type of lens used for viewing.

This is one of the most important parts of a compound microscope, because this ocular lens is the compounding lens that re-magnifies the produced image of the first lens, or the objective lens. Each ocular lens typically has a magnification of 10x to 15x. Although, you will sometimes find compound microscopes with a variable magnification of 5x to 30x.

Number of lenses

The microscope’s eyepiece can either have one, two, or three ocular lenses.

Monocular –  A monocular eyepiece is somewhat rare, since it’s difficult to use as you have to close one eye when looking at the specimen, and you can’t look at all when using a camera to capture the magnified image. However, the good thing about it is it makes for a lightweight microscope, and it’s the most affordable option.

Binocular – Meanwhile, a binocular eyepiece is the most common when it comes to compound microscopes. You can view the specimen easily with both eyes, so it’s comfortable to use. This kind of compound microscope is what you’ll see in most classrooms and science laboratories.

Trinocular: finally, there are also trinocular eyepieces, which means there are three different lenses on three eyepiece tubes, so you can look at the specimen while another person views it simultaneously, or while you use a camera to capture the image you’re viewing. It’s an excellent compound microscope for teaching, but it’s the most expensive option.

Eyepiece tube

The eyepiece tube is a long metal tube that holds the eyepiece at the upper end, and is attached to the microscope head at the bottom. It’s a long piece of a hollow metal tube that enables light to pass through, letting you be able to view the magnified image of the specimen.

It extends to the inside of the head and connects to the objective lens on the revolving nosepiece. Depending on whether the eyepiece is monocular, binocular, or trinocular, the eyepiece tube may feature adjustment dials to improve the user’s viewing experience.

Diopter adjustment

In the case of binocular and trinocular eyepieces, a diopter adjustment ring is important. It’s a small dial located right below the eyepiece, and it can be used to change the focus of either eyepiece.

This is important if you have an inconsistent vision between your eyes, as well as if you’re using a camera, or if another person is viewing the specimen with you.

Interpupillary adjustment

Another feature of a trinocular eyepiece is its interpupillary adjustment, which basically means the eyepiece tubes can swivel at a certain direction to accommodate differences in eyesight of two individuals using the microscope at the same time.

Each eyepiece tube can be adjusted to an angle of 30 to 45 degrees by adjusting the hinge adjustment and sliding, so you can find a comfortable viewing position especially if you are using a camera or working with another person.

Revolving nosepiece

At the lower end of the head is the revolving nosepiece, which is a circular rotating turret with at least three to five prongs that hold an objective lens of varying magnifications for each prong.

This nosepiece can be adjusted in such a way that an objective lens is fully aligned with the eyepiece as it clicks into place, allowing you to view the specimen through the lens you have selected.

Objective lenses

The objective lens is the primary optical lens of any type of light or bright field microscope. These are exposed lenses located at the lower end of the revolving nosepiece, and can either be forward or rear-facing.

Objective lenses have various classifications and specifications, as well as different magnifications, which can range in power from 4x to 100x. These are the closest lenses to the specimen, making them one of the most important parts of the microscope, but also the most sensitive.

Thus, it’s important to be careful when using and cleaning these lenses, and to avoid them coming into contact with the specimen or other objects other than a lens paper.

The body

The microscope’s body (also called the frame) is its entire middle section, which holds the entire microscope together by connecting the head to the base, as well as serves as its arm, which is how you can carry the microscope when transporting it to and from its storage area to your work table.

This section of the microscope houses several different parts and controls, the most important being the mechanical stage, which is where the specimen is loaded for viewing. The body also hosts the fine and coarse adjustment knobs.

Here are the different parts you can find on the body:

Adjustment knobs

A common feature of compound light microscopes is the presence of a coarse adjustment knob and a fine adjustment knob, which are what you use to adjust and refine the focus of the microscope, so you can see the specimen image as clearly as possible.

The coarse adjustment is what brings the image into general focus, whereas the fine adjustment further refines this focus in order for you to see the intricate details of the specimen. When using these knobs, it’s important to start with the coarse adjustment and focus the microscope as clearly as possible, before moving on to the fine adjustment to perfect the focus.

Coaxial knobs

Nowadays, compound microscopes are built with coaxial knobs, which means the coarse and fine adjustment rests on the same axis, with the coarse adjustment on the inside and the fine adjustment on the outside.

It’s arguably easier to use, since you’re only working with one knob to focus the microscope.

Specimen stage

Another important part of the microscope that can be found on the main body is the stage or specimen holder. This is a flat square platform where a glass slide containing the specimen is placed, so it can be viewed through the lenses.

The stage may look like a simple square piece of metal, but it actually has a lot of different components that make loading and viewing the specimen as safe and easy as possible.

Aperture

Right in the middle of the stage is a small circular hole called the aperture. This is the opening that allows light from the light source or illuminator to shine and pass through the specimen, and then reach the objective lenses.

Loading the specimen slide the right way is important. This should be done in such a way that the specimen falls right over the aperture, so that the entire specimen can be illuminated, and therefore viewed under the microscope.

Stage clips

On both edges of the stage are a set of stage clips, which are essentially pieces of metal that can be lifted lightly in order to fit the specimen slide and hold it securely in place.

Not all compound microscopes have stage clips. These can mostly be found on older models, and especially on those with a manual stage, since you will need to adjust the position of the specimen slide manually to view different parts of the specimen, rather than adjusting the stage itself.

Stage control

Compound microscopes with a high magnification of 400x or higher normally feature a mechanical stage, meaning, it has a dedicated stage control that is used to adjust the level of the stage in order to get the specimen as close to the objective lens as possible, without the two actually coming into contact with each other.

The stage control is a knob that can move the stage to a certain degree up, down, left, and right, so that the specimen is perfectly aligned with the objective lens.

Rack stop

The rack stop is a small piece of screw located at one end of the stage nearest to the main frame. Its main function is to prevent the stage from getting too close to the objective lenses and the specimen coming into contact with the lens.

It’s typically already pre-set by the factory and doesn’t need to be adjusted when using the microscope.

The base

The bottom section of the microscope is called the base, which is primarily what makes the microscope stable, upright, and balanced, and what enables it to carry its own weight. For this reason, the base is normally weighted.

It also contains a few necessary parts that are essential in the microscope’s function. These include the microscope’s light source and its adjustment mechanisms, as well as the microscope’s main switch.

Here are the different parts you can find on the base:

Light source

The most important part of a compound microscope that you’ll find at its base is the light source or illuminator, which is what provides the light that illuminates the specimen and lets you see the magnified image through the eyepiece.

This light source is essential for all light or bright field microscopes. Old compound microscopes typically make use of a mirror that reflects external light from your surroundings, while most microscopes nowadays use a low voltage halogen bulb with a continuous variable lighting. Newer models of compound microscopes may feature bright LED light bulbs.

Condenser

Above the illuminator and under the stage is a condenser, a small device that collects and focuses the light from the illuminator onto the specimen, in order for the maximum amount of light to reach the specimen in such a way that the light isn’t scattered but focused onto the specimen.

It may feature a condenser focus knob, which is used to move the condenser up or down to better focus the light.

Iris diaphragm

In between the condenser and the stage is a smaller device called the iris diaphragm. It adjusts and controls the amount of light that reaches the specimen. Lower contrast specimens like transparent and opaque objects need more light to show the details clearly, and the iris diaphragm is what’s used to increase the quantity of light that illuminates the specimen.

Higher-end modern compound light microscopes will normally feature an Abbe condenser with the iris diaphragm, which work hand in hand in controlling the quantity and focus of the light.

Power switch

Finally, the microscope base is also where you can find the power switch, which is what turns the illuminator on and off. It’s important to remember to keep the switch turned off whenever the microscope is not in use.

How to use a compound microscope

Parts and Function of the Compound Light Microscope
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Now that you know all the different parts of a compound microscope, it’s time to understand how to operate it correctly. Below are the steps in using a compound light microscope:

  1. If the microscope is in storage, carry it by lifting the microscope by the arm and support the weight by placing your other hand under the base. Place the microscope on your work table. With the microscope arm facing your direction, turn the coarse adjustment knob to raise the body tube to a comfortable degree.
  2. Next, rotate the revolving nosepiece until the low power objective lens clicks into place. Look through the eyepiece to ensure that you have a clear line of sight. Turn on the illuminator, and adjust the light by turning the condenser knob and the iris diaphragm until a bright circle of light shines through the aperture.
  3. Prepare the specimen on a glass slide, and place a cover slip on top. This will protect the specimen and the objective lens from each other, and make it easier to load, remove, label, transport, and store the specimen later on.
  4. Mount the slide onto the stage, with the specimen resting directly above the aperture. Look through the eyepiece to check whether the specimen is visible, and secure the slide with the stage clips, or adjust the stage using the stage control.
  5. Readjust the coarse focus to lower the body tube until the objective lens is nearly touching the cover slip of the specimen. Do this by looking at the side of the microscope. Then, look through the eyepiece and refine the adjustment knobs to better focus the image of the specimen.
  6. If you need a higher magnification power, carefully rotate the nosepiece to shift into the high power objective lens until it clicks into place. Afterward, readjust the coarse and fine focus knobs to refocus the specimen image.
  7. When you’re done, lower the stage, remove the specimen, and reset the nosepiece into the low power objective. Turn the power switch off, cover the microscope with a dust protector, and return it safely to its storage place.

Overview

A compound microscope is a type of microscope that has compound lenses, and operates through light microscopy techniques. It is a high magnification and high power microscope suitable for viewing minute details of small specimens that are invisible to the naked eye.

The parts of a compound microscope can be categorized into two- the optical components, which are the objective lenses and the ocular lenses. All are located at the head of the microscope, and the structural components, which include the adjustment knobs and the light source, which can be found throughout the main frame and the base of the microscope.

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