An optical microscope creates an image using light and glass lenses, whereas an electron microscope creates an image using a beam of electrons focused by electromagnetic lenses in a vacuum. This allows the electron microscope to have incomparably greater resolution and reveal structures at the nanometer level, but it cannot observe living cells. An optical microscope is simpler, less expensive, and can display samples in color, even living ones.
To sum it up
- Image source: optical – visible light, electronic – electron beam.
- Permission: optical - approximately 0.2 µm (200 nm), electronic - nanometers, and in the best cameras - fractions of a nanometer.
- Samples: In the optical method, living cells can be observed; in the electronic method, the sample is placed in a vacuum and must be specially prepared.
- Availability: Optical instruments are available in every school laboratory, and electronic instruments are available in specialized laboratories.
Operating principle: light and electrons.
В optical (light) microscope Light passes through or reflects from the sample, and a lens system—an objective and an eyepiece—magnifies the image. We see it directly with our eyes or through a camera. The image is colored, and samples are often additionally stained to highlight details such as cell nuclei.
В electron microscope Instead of light, a beam of electrons is used, and instead of glass, electromagnetic lenses are used. Electrons are easily scattered by air molecules, so the microscope's column must be in a vacuum. The image cannot be seen with the naked eye through the eyepiece; it is created on a screen or detector and is black and white; color images obtained with electron microscopes are colored using a computer.
The first electron microscope was created in the early 1930s by Ernst Ruska and Max Knoll. For this work, Ruska received the Nobel Prize in Physics in 1986.
Magnification and resolution are the most important differences.
More important than the increase itself is resolving power , which is the smallest distance between two points that can still be distinguished. In an optical microscope, this limitation is determined by the wavelength of visible light—approximately 0.2 µm (200 nm) . Therefore, the useful magnification of a classic light microscope is typically around 1000–1500x; higher magnification will only result in a larger, but blurrier, image.
Electrons have a much shorter wavelength than light, so an electron microscope can resolve details of the order nanometers , while the best transmission microscopes can resolve details down to fractions of a nanometer, i.e., individual columns of atoms. This allows for magnifications of hundreds of thousands or even over a million times.
In practice, an optical microscope allows us to see cells, cell nuclei, bacteria, and larger organelles. An electron microscope allows us to detect viruses, ribosomes, and the detailed structure of membranes and mitochondria. There are also fluorescence-based methods (so-called super-resolution microscopy), which allow us to bypass the classical resolution limit of light, but require specialized equipment.
Types of electron microscopes: TEM and SEM
- Transmission electron microscopy (TEM) – electrons pass through a very thin sample. This allows for high-resolution imaging of the internal structure of cells and materials.
- Scanning electron microscopy (SEM) The beam moves across the sample's surface, and detectors record the electrons ejected or reflected from it. This allows for the acquisition of characteristic "three-dimensional" images of surfaces, such as insect eyes or pollen.
A type of transmission electron microscopy is cryo-electron microscopy , in which samples are rapidly frozen rather than chemically fixed. This technique allows the structure of proteins and viruses to be studied in a state close to their natural state; its inventors were awarded the Nobel Prize in Chemistry in 2017.
Optical and Electron Microscopes - Comparison Chart
| Characteristic | Optical microscope | Electron microscope |
|---|---|---|
| Image source | Visible light | Electron beam |
| Lenses | Glass | Electromagnetic |
| Resolution | Approximately 0.2 µm (200 nm) | Nanometers and fractions of a nanometer |
| Useful increase | About 1000-1500 times | Hundreds of thousands and more |
| Work environment | Air | Vacuum |
| Living cells | Yes | NO |
| Painting | Colourful, seen through the eyes or camera. | Black and white image on screen (color added by computer) |
| Sample preparation | Simple (glass, sometimes stained glass) | Complex processes (fixation, dehydration, cutting, spraying or freezing) |
Sample preparation and limitations
When using an optical microscope, a drop of water with the specimen on a coverslip is often sufficient. Movement of protozoa, cell division, and cytoplasmic flow can be observed. Limitations include resolution and low contrast of transparent structures, which can be improved by staining or phase-contrast microscopy.
In an electron microscope, the sample is placed in a vacuum and bombarded with electrons, so living cells cannot survive this process. Biological samples for TEM must be fixed, dehydrated, and cut into very thin sections; for SEM, non-conductive samples are usually coated with a thin layer of metal. Each of these steps can lead to the appearance of artifacts—changes not present in the natural specimen.
What is each microscope intended for? Application areas.
- Optical microscope – biology lessons, laboratory diagnostics (e.g. blood smear examination, histopathological examination), observation of living cells and microorganisms, quality control in industry.
- Electron microscope – study of the structure of viruses and organelles, protein structure, materials science, nanotechnology, semiconductor industry, analysis of cracks and metal surfaces.
Optical microscopes are the preferred choice for home and school use. Electron microscopes are large and expensive instruments that require a dedicated room, vacuum, and qualified personnel. They are used in universities, research institutes, and industrial laboratories.
Frequently Asked Questions (FAQ)
How many times does an optical microscope magnify an image, and how many times does an electron microscope magnify an image?
A classic optical microscope provides useful magnification of approximately 1000–1500 times. An electron microscope magnifies images hundreds of thousands, or even more than a million times. However, more important than magnification is resolution: around 200 nm in optical microscopes and nanometers or less in electron microscopes.
Why can't living cells be seen with an electron microscope?
The sample is placed in a vacuum and bombarded with an electron beam. It is usually fixed and dehydrated before analysis. Living cells cannot survive in such conditions.
Can a virus be seen under an optical microscope?
The vast majority of viruses are smaller than the resolution limit of a light microscope (approximately 200 nm), so their structure cannot be seen with a standard optical microscope. An electron microscope is used for this purpose.
What is the difference between a transmission electron microscope and a scanning electron microscope?
In transmission electron microscopy (TEM), electrons pass through a thin sample, revealing its internal structure. In scanning electron microscopy (SEM), a beam of electrons moves across the surface of the sample, creating an image of its shape, often with a three-dimensional effect.
Why are photographs taken with an electron microscope in color?
An electron microscope records images in grayscale. The colors we see in publications and media are added by a computer to highlight individual structures.
See also
- What is the difference between a telescope and a regular telescope?
- What is the difference between an academy and a university?
- What is the difference between complete and basic morphology?
- What is the difference between an emission spectrum and an absorption spectrum?