A microscope is a scientific instrument used to magnify and observe tiny structures that aren’t visible to the naked eye. They are necessary tools in different branches of science, from physics and chemistry to biology, medicine, and materials science.
Did you know the first simple microscope was developed by Dutch scientist Antonie van Leeuwenhoek in the late 16th century? It was a single-lens microscope containing a tiny glass bead (mounted on a metal plate) that served as a lens.
Why are microscopes important?
Microscopes are essential for several reasons. They allow researchers to examine the structure of cells and tissues, observe the tiniest details of animals and plants, and understand how microorganisms work.
Different types of microscopes are used to study microorganisms, diagnose diseases, and inspect materials for defects.
In industrial settings, microscopes are used for quality control purposes. They help measure dimensions, inspect the integrity, and ensure adherence to specific standards at a microscopic level. They also aid in analyzing material structures and detecting contaminants in critical components.
Advanced microscopes, such as electron microscopes and scanning probe microscopes, have allowed engineers and scientists to study the intricate properties of materials in detail. This has led to the development of new materials, electronics, and nanotechnology (especially in the past few decades).
While microscopes can vary significantly in terms of design and magnification techniques used, there are some common materials found in all optical instruments.
Below, we’ve featured all the key parts of a microscope along with their functions.
Table of Contents
1. Ocular Lens (Eyepiece)
Located at the top end of the microscope, it is the lens through which viewers directly observe the sample. It magnifies the image created by the objective lens.
In simple terms, the ocular lens is a compound lens (two or more lenses stacked together) designed to provide a clear, magnified view of the sample.
The ocular lens is typically a compound lens system consisting of multiple lenses designed to provide a clear and magnified view of the specimen. It is usually composed of two or more lenses stacked together. These lenses are carefully arranged to correct for aberrations and provide optimal image quality.
- Typically made of plastic or glass
- Usually mounted in a rotating current
- Various ocular lenses are available with different magnifications and field of views
- Some can reduce glare and reflections to improve image quality
Their magnification power is denoted by “X,” which indicates the factor by which the image is magnified when viewed through the ocular lens.
2. Objective Lenses
The objective lens captures and magnifies the details of the sample. When light (from the microscope’s illumination source) passes through the sample, the objective lens focuses and converges the light rays to form a real, magnified image of the sample.
Like an ocular lens, the objective lens is typically a compound lens arranged in a specific configuration. Its magnification power is also dented by “X.”
Types of objective lenses
- Scanning objective lenses have 4X or 10X magnification to get a general overview of the sample.
- Low-power objective lenses have 20x or 40x magnification to observe more detail of the sample.
- High-power objective lenses have 100x or 400x magnification power to observe the smallest details.
It is important to note that the magnification power of a microscope is measured by multiplying the magnification power of the objective lens and the magnification power of the ocular lens.
For example, if the ocular lens has a magnification power of 20X and the objective lens has a magnification power of 100X, the total magnification of the microscope is 2,000X.
3. Eyepiece Tube
Eyepiece is typically a cylindrical tube that connects the ocular lens to the objective lens system. It serves as an optical pathway for the light to travel from the objective lens to the ocular lens, enabling viewers to see the magnified photo of the sample.
It also ensures that the optical axis of the ocular lens aligns with the optical axis of the objective lens for consistent and precise observation.
Many advanced microscopes have filters, such as polarizers or color filters, within the eyepiece tube. These filters allow viewers to reduce glare, improve contrast, and selectively filter light wavelengths to reveal specific structures or features in the sample.
4. Body Tube
The body tube allows light to travel from the objective lens to the eyepiece tube. It is made of plastic or metal and is usually about 4-12 centimeters long, depending on the microscope design.
While the eyepiece tube refers to the upper section of the tube that includes the ocular lens, the body tube is the lower section that contains the optical elements between the objective lens and the eyepiece.
Modern microscopes have a modular design, which makes it easier to interchange or adjust the body tube. This flexibility is helpful because it allows users to customize the instrument according to their specific needs or the type of observation they want to perform.
5. Revolving Nosepiece
A revolving nosepiece is a rotating mechanism usually located below the body tube and above the stage. It holds and allows easy interchangeability of multiple objective lenses.
It is designed to provide convenience and efficiency in observing samples at different magnification levels or with different imaging methodologies.
Viewers can simply rotate the nosepiece to quickly switch between different objective lenses (without having to physically detach and replace them). This feature saves a lot of time and effort.
The stage is a flat, sturdy surface located beneath the objective lenses. It’s a fundamental part of a microscope that provides a platform to hold and position the sample being observed. It has a hold in the center to allow light (from the illumination source) to pass through the sample.
Two main types of stages
- Simple Mechanical Stage allows viewers to move the sample back and forth and side to side.
- Traversing Stage is equipped with a motor that allows viewers to move the sample precisely and smoothly in any direction.
A few specialized microscopes contain sophisticated stage platforms to facilitate certain techniques. For instance, inverted microscopes used in cell culture have heated stages to maintain a specific temperature for live cell imaging.
7. Stage Clips
These are small, spring-loaded clips located on the sides of the stage. They are designed to hold the sample in place and prevent it from moving during observation.
Stage clips ensure the sample remains within the field of view and in focus. They can be extremely useful when observing thin, flat specimens mounted on glass slides (as they prevent the slide from sliding out of the focal plane).
Some modern microscopes have motorized stages or automated sample holders instead of manual stage clips. However, their primary task remains the same — securing the sample in place during observation.
The arm, also referred to as the microscope frame or body, is a structural component that provides support and stability to the optical system. It is usually an angled or curved part of the microscope, connecting the base and head.
It ensures that the eyepiece, objective lenses, and other optical components are positioned and aligned for precise imaging and analysis.
The arm is usually made of sturdy plastic or metal to provide stability and strength to the microscope. It is built to be rigid and resistant to vibrations that could impact the image quality.
The base is the lowermost part of the microscope that rests on a tabletop or other flat surface. It is designed to have a wide surface area and sufficient weight to prevent the instrument from tipping over or moving during use.
The base is typically made of heavy-duty materials, like dense plastic or metal, to provide the necessary weight and structural integrity to keep the instrument stable. It is often coated with a non-slippery material or attached with rubber feet to increase its grip on the surface and prevent accidental slippage.
Some microscopes come with detachable bases or foldable legs that facilitate compact storage, easy portability, and transportation.
10. Light Source
The light source in a microscope provides the necessary light for illuminating the sample being observed. It allows viewers to accurately observe the details and features of the sample.
Most light sources offer brightness or intensity settings, allowing users to control the amount of light reaching the sample. By adjusting these settings, users can achieve optimal contrast and image quality and prevent underexposure or overexposure of the sample.
Main types of light sources
- Transmitted light sources are located beneath the stage and shine light through the sample from below
- Reflected light sources are located above the stage and direct light onto the sample from above
Advanced microscopes use Köhler illumination — a technique that ensures uniform illumination across the sample.
Some microscopes employ specialized light techniques such as phase contrast microscopy or fluorescence microscopy. These techniques require particular light sources and filters to improve the contrast and details in transparent samples or excite and visualize fluorescent molecules, respectively.
The rheostat is a knob or dial that controls the intensity of the light source. More specifically, it’s an adjustable resistor that regulates the amount of electric current flowing through the illumination system.
Viewers can adjust the rheostat to increase or decrease the light brightness for optimal illumination of the sample. For example, if the sample is too dark, users can turn the rheostat to a higher setting to make the image brighter.
It is compatible with various types of light sources, including LEDs and halogen lamps. It is usually installed in both transmitted and reflected light microscopy setups.
12. Coarse Knob
The coarse knob is used to adjust the position of the stage to bring the sample into rough focus.
Located on the arm of the microscope, this knob can be turned clockwise or anticlockwise. When it is turned clockwise, the stage moves up, and when it is turned anticlockwise, the stage moves down.
By adjusting the coarse knob, users can quickly bring the sample into view and prepare it for finer adjustments.
13. Fine Focus Knob
As the name suggests, the fine focus knob enables precise adjustments of the focus to achieve clear, sharp images of the sample. It’s a smaller knob located above or near the coarse knob.
Unlike the coarse knob that allows for larger and quick adjustments, the focus knob allows for smaller, controlled movements. These minute adjustments bring the sample into sharp focus and reveal fine details.
It is important to note that the coarse knob and the focus knob work together to achieve the desired focus level. The coarse knob is used for rough focusing, bringing the sample into view, whereas the focus knob is used for precise adjustments to bring the sample into sharp focus.
Condenser is an optical component that collects and directs the light (from the microscope’s light source) onto the sample. Located beneath the stage and above the light source, its primary function is to provide even and controlled illumination for the sample.
It uses a combination of mirrors and/or lenses within its optical system to focus the light into a specific area.
- Achromatic condenser is used in general-purpose microscopy
- Darkfield condenser is designed to enhance contrast and visualize transparent or unstained specimens
- Phase contrast condenser is used for observing transparent or low-contrast specimens like live cells
- Polarizing condenser is used to observe specimens that exhibit polarization effects
- Differential interference contrast condenser is used to enhance contrast and 3D visualization of transparent samples
The condenser also contributes to the microscope’s numerical aperture (NA). The NA shows the ability of a microscope to collect and resolve fine details. The higher the NA, the greater the resolving power and better image quality.
Nine-blade Diaphragm | Image credit: Wikimedia
A diaphragm is an opaque disc with an opening (aperture) at its center. It contains thin, overlapping blades that form an adjustable circular or semicircular opening. The blades can be closed or opened by rotating a dial or adjusting a lever.
It is used to control the amount of light that passes through the microscope. It is located between the light source and the sample.
Functions of the diaphragm
- Controls the amount of light passing through the microscope
- Help in achieving the ideal balance of light and contrast
- Optimize the image for different types of samples
By adjusting the diaphragm, users can change the depth of field. For example, a larger aperture decreases the depth of field, meaning only a limited plane of focus appears sharp, but it enhances contrast and resolution of specific areas of interest.
A smaller aperture, on the other hand, decreases the depth of field, which means more of the specimen appears in focus. This can be useful when examining specimens with complex structures or uneven surfaces.
16. Stage Micrometers
These are calibration tools used to measure the size of the sample or distances observed through the microscope. They are usually made of glass or plastic and have a scale that is divided into very small units.
The scale (calibrated in micrometers) is used as a reference standard for measuring the size or magnification of samples.
- Allows users to accurately measure the sample size
- A relatively inexpensive tool
- Difficult to align the scale on the stage micrometer with the image of the sample
- Scale can be difficult to read
There are various forms of stage micrometers, and they come with different scales. Some have single scales, while others have multiple scales or patterns suitable for specific measurement techniques or applications.
17. Binocular or Trinocular Head
Head refers to the part of the microscope that holds the eyepieces and allows users to observe the magnified image of the sample. There are two main types: binocular and trinocular heads.
A binocular head has two eyepiece tubes positioned at a comfortable distance from each other to match the viewer’s interpupillary distance. It offers a more natural viewing experience and is comfortable for long periods of observation.
A trinocular head features an additional third tube called the trinocular port or phototube. It allows users to attach a camera or other imaging devices to record videos of the observed sample. This is useful for documentation, research, or sharing visual data.
18. Filter Holder
Some microscopes have a filter holder within their optical pathway. It offers a convenient and secure way to incorporate filters into the microscope system.
The filter holder may contain a frame or cartridge to accommodate one or more filters, depending on the microscope model and configuration.
Filters are used to modify the properties of light passing through the microscope, such as its intensity, color, or polarization. Viewers can place filters to increase contrast, reduce glare, or isolate certain colors.
19. Immersion oil
Immersion oil is a specialized optical liquid used in microscopy to improve the clarity of magnified images. It fills the air gap between the objective lens and the sample, minimizing the refraction of light rays as they pass through the different media (air, glass, and oil).
Immersion oil has a refractive index that is very close to the refractive index of glass. This means when light rays pass from the objective lens to the sample, there is very little refraction. And this less refraction results in a more accurate and brighter image.
However, not all microscopes require the use of immersion oil; those with lower magnification objectives can provide decent image quality without it.
More to Know
Are microscope parts replaceable?
Yes, individual parts of a microscope can be replaced or upgraded as needed. The most common replaceable parts are objective lenses, eyepieces, illumination components, mechanical stages, stage clips, focusing knobs, and diaphragms.
The availability of replacement parts varies depending on the specific microscope brand, model, and age. In most cases, manufacturers or authorized dealers offer replacement components for their products.
What’s the most advanced microscope as of now?
It’s hard to determine the most advanced microscopic instrument — various powerful microscopes have been developed for specific research needs. For example,
- Titan Krios is a transmission electron microscope that allows scientists to analyze the structural features of proteins, viruses, and other biomolecular complexes.
- Lattice light-sheet microscope with adaptive optics, on the other hand, allows scientists to study cellular dynamics, neuroscience, developmental biology, and other areas that require non-invasive imaging of living samples.
Both technologies have made significant contributions to their respective field and continue to push the boundaries of imaging capabilities.
Future demand and sales trends for microscopes
According to the Grand View Research report, the global microscope market size will reach $20.4 billion by 2030, growing at a CAGR of almost 8% from 2023 to 2030.
The key factors behind growth include the high demand for technologically advanced magnification instruments and the rapidly growing semiconductor industry. The development in the microscopy field to promote research activities will contribute to the increasing product demand.
Moreover, easy sample preparation techniques, faster imaging performance, and the integration of advanced techs like Extended Ultraviolet Lithography (EUVL) and Deep Learning Models are also expected to contribute to the growth of the industry.