Microscope Parts And Functions

The word microscope comes from the Latin word Microscopium meaning little eye or peephole. Microscopes are instruments that magnify objects.

They are widely used in science, medicine, biology, chemistry, engineering, and other fields. A microscope consists of two main components: the objective lens and the eyepiece.

Microscope Parts And Functions

The objective lens focuses light onto the specimen being studied. The eyepiece magnifies the image of the specimen.

In this article, we will be discussing various parts of a microscope and its functions. We will also discuss how to use a microscope for different purposes.

Objective Lens

An objective lens is an optical component that projects an object into focus on the plane of the aperture stop (also called the diaphragm).

It has both refractive power and magnification. Magnification is the ratio between the size of the object as seen through the objective lens and the size of the same object as it appears at the focal length of the objective lens.

Objective lenses can have either positive or negative powers. Positive objectives have more than one focal point. Negative objectives only have one focal point.

A typical objective lens has a front convex surface called the meniscus. This is where most of the light rays converge. The back surface is flat and perpendicular to the axis of the lens.

To increase the resolution of the image, the diameter of the objective lens must be larger than the diameter of the pupil.

An objective lens with a large diameter is known as a long working distance objective lens.

The objective lens focuses an image onto the sensor. The objective lens is also used for viewing purposes.

Objective Lenses come in two varieties: single-element and multiple elements. Single-element lenses contain only one element. Multiple-element lenses contain two or three elements.

Single Element

Single element lenses contain only one element that works together to form the entire objective lens system. They are typically used for low magnification applications such as macrophotography.

Multiple Elements

Multiple element lenses contain more than one element. Each element works together to focus the light.

Multiple element lenses can have any number of elements. They are typically used at higher magnifications.

Aperture Stop

An aperture stop is a device that controls the amount of light entering the objective lens. The aperture stops are usually made up of blades or discs.

The blades are placed inside the objective lens. The disc is placed outside the objective lens. Both types of aperture stop controlling the amount of light passing through the objective lens.

There are several types of aperture stops. These include iris diaphragms, iris shutters, iris plates, and iris wheels.

Iris Diaphragms

Iris diaphragms are circular openings cut out of the edge of the blade. The opening is smaller than the diameter of the objective.

Light enters the objective lens and passes through the opening in the blade. As the blade rotates, the light travels around the circumference of the blade.

When the blade is closed, the light is blocked by the blade. When the blades are open, the light passes through the opening.

Iris Shutters

Irises are small rectangular pieces of glass that slide across the path of light. When they are fully open, there is no obstruction to the light. When they are completely closed, the light is stopped.

Iris Plates

Iris plates are disks of glass with holes drilled in them. The disk is placed over the objective lens. The holes are smaller than the diameter of an objective lens.

Light passes through the holes and then through the objective lens. When the plate is rotated, the light travels around its perimeter.

Iris Wheels

Irises are circular disks of glass. There are many variations of irises, but all work similarly. The wheel is placed over the objective.

A hole is drilled in the center of the wheel. The hole is slightly larger than the diameter of the objective.

Light passes through the hole and then through the objective. When the wheel is turned, the light travels around it.

Lens Mounts

Most microscope objectives are mounted on a holder. This holder is called a lens mount. Lens mounts come in different sizes.

Some mounts hold only one lens. Others can hold multiple lenses. Different mounts allow you to change the focal length of your lens.

Focusing Mechanism

A focusing mechanism allows you to move the objective lens closer to or further from the sensor.

It does this by moving the objective lens along its axis. Most focusing mechanisms use screws or levers to accomplish this task.

Zoom Lenses

A zoom lens changes the magnification of the image without changing the size of the field of view. Zoom lenses are often used when working at high magnifications.


An eyepiece is a round window located in front of the objective lens. Through the eyepiece, you see the object being viewed. You can adjust the position of the eyepiece using a knob or lever.

Diopter Adjustment

To determine how much correction is needed, you need to know what type of diopter adjustment you require. Diopters are either positive or negative.

Positive diopters correct for myopia (nearsightedness). Negative diopters correct for hyperopia (farsightedness).

Body Tube (Head)

The body tube is the main part of the microscope. It holds everything else. The body tube contains the illumination source, condenser, eyepieces, stage, and other accessories.


The arm is attached to the top of the body tube. It contains the motor drive for turning the turret. The arm holds the objective lens.


The turret is where the objective lens sits. It turns about a vertical axis. The turret rotates to align the objective with the sensor.


The stage moves the sample up and down. In some microscopes, the stage is stationary. In others, the stage slides back and forth.

Illumination Source

The illumination source illuminates the specimen. It may be a lamp or a fiber optic cable.



A condenser collects light from the illumination source and directs it toward the objective lens.


The sensor converts the light information into electrical signals. These signals are then processed by the computer.

Fine Adjustment

You can fine-tune the microscope’s settings so that it performs exactly as expected. Fine-tuning includes adjusting the brightness, contrast, and color balance.

Specimen Or Slide

Slides are thin sheets of glass or plastic. Specimens are placed on the slide. Slides are used for viewing cells and tissue specimens under the microscope.

How Does A Compound Microscope Work?

Compound microscopes have two parts: an upright microscope and a dissecting microscope. The upright microscope has all the features of a standard microscope.

A compound microscope also has a dissecting scope. The dissecting scope is like a small telescope. It is set above the upright microscope.

When you look through the dissecting scope, you can see the specimen. The dissecting scope provides magnification similar to that of binoculars.

How Do I Use A Compound Microscope?

Use a compound microscope to examine objects such as plants, insects, and animals. To use a compound microscope, follow these steps:

  1. Place your specimen on a slide.
  2. Put the slide on the stage of the microscope.
  3. Look through the dissecting scope.
  4. Move the slide around until you find something interesting.
  5. Focus the microscope.
  6. Take pictures or record videos.

Final Thoughts

There are many types of microscopes available today. Some are expensive while others are inexpensive. All microscopes work in the same way.

They magnify images. However, there are differences between them. For example, some microscopes have more than one focus setting.

Others have different lenses. Still, others have different stages. You should choose a microscope based on its features. If you want a good quality microscope at a reasonable price, consider purchasing a compound microscope.

Jennifer Dawkins