Microscopes

At the base of the microscope, you’ll typically find a light source—usually an LED or a halogen lamp. The intensity of this light can be adjusted with a control knob on the side. The reason it’s called a light microscope is that it uses visible light to illuminate the specimen, providing a bright, stable beam that passes through the sample, allowing you to observe it clearly.

Above the light source sits the condenser, a lens system designed to focus the gathered light onto the specimen. Similar principles apply in refracting telescopes, where lenses also gather and focus light. By adjusting the condenser’s position and aperture, you can control the contrast and sharpness of the image. This step is crucial for getting a clear, detailed view.

Above the condenser is the stage, where you place your specimen mounted on a slide covered by a cover slip. The stage often allows fine movement in the X and Y directions, enabling you to scan across different areas of your specimen without shifting the microscope itself.

Above the stage are the objective lenses, which provide the primary magnification. They are mounted on a rotating nosepiece (revolver head), allowing you to switch between different magnification levels quickly. On my particular microscope, I have 4x, 10x, 40x, and 100x objectives. These objectives, combined with the eyepieces (oculars), determine the total magnification.

Above the objectives are the eyepieces, also called oculars. These are the lenses you look through. Their magnification (often 10x, 15x, or another value) further multiplies the magnification provided by the objective lens. For example, using a 100x objective with a 10x eyepiece results in a total magnification of 1000x.

To bring the image into crisp focus, microscopes usually have coarse and fine focusing knobs. By adjusting the vertical position of the stage relative to the objectives, you can achieve a sharp image of the specimen.

The microscope shown above differs slightly from what I described. It has two light sources: one illuminating from below (transmitted light) and another from above (reflected light), allowing for the observation of both transparent and opaque samples.

• Transmission Electron Microscope (TEM): Electrons pass through a very thin specimen. The interactions of these electrons with the sample form an image with extremely high resolution and magnification.

• Scanning Electron Microscope (SEM): Instead of passing through the sample, an electron beam scans across the surface. Detectors measure the interactions of the electrons with the surface, creating a detailed, three-dimensional-like image of the specimen’s topography.

If you want to learn more about how electron microscopes work, I recommend watching this video (in English): How Electron Microscopes Work.

In an electron microscope, the electron gun acts as the “light source.” Electrons are accelerated by electric fields to extremely high speeds, often approaching a significant fraction (about 70%) of the speed of light in vacuum. This is necessary to achieve a clear, undistorted final image. Without this high-speed acceleration, the resulting image would be blurry and of poor quality.

After leaving the electron gun, the electron beam is manipulated by a series of electromagnetic lenses. Unlike glass lenses in optical microscopes, these lenses are coils of wire that generate magnetic fields, steering and focusing the electrons along the correct path. This ensures a fine, stable, and highly controlled electron beam.

The electrons travel through a vacuum chamber inside the microscope. This vacuum environment is essential because it prevents electrons from colliding with air molecules. Any such collision would scatter the electrons, blur the image, and reduce the instrument’s resolution. The vacuum ensures a clean, straight electron path.

The electron beam interacts with the specimen—electrons may be scattered, absorbed, or transmitted depending on the sample’s structure and composition. These interactions form the basis of the image. Different materials, layers, and thicknesses show up distinctly, providing insight into the sample’s internal structure.

Signals from the electron-specimen interaction are picked up by various detectors (fluorescent screens, digital detectors) and translated into an image. The resulting images can have remarkably high resolution, enabling researchers to see details at the atomic or molecular level.

Extended Note Microscopy, whether optical or electronic, opens up entire worlds invisible to the naked eye. With light microscopes, we can examine cells, tissues, microorganisms, and crystals with relative ease and affordability. Electron microscopes go even further, revealing intricate details of materials, viruses, and molecular structures at astonishing resolutions, going beyond hundreds of thousands of magnifications.

The usage of microscopes is pivotal and must-use in fields such as biology, nanotechnology, and even in semiconductor research.