The Short Answer
Biologists use microscopes from three broad families:
- Light (optical) microscopes, which use visible light and glass lenses.
- Electron microscopes, which use a beam of electrons and magnetic lenses.
- Scanning probe microscopes, which trace a fine tip across a surface.
Exam questions often ask for “the three types of microscopes used in biology”. The usual expected answer is light microscopes, transmission electron microscopes (TEM) and scanning electron microscopes (SEM). When the question asks for “four main types”, the answer is often compound light, stereo, TEM and SEM. Syllabuses differ, so check which list your course uses.
The rest of this article goes through each family and explains what each type is best at. For background on the basic ideas, see our introduction to microscopy.
Light Microscopes
Light microscopes are by far the most common type in biology. They’re relatively affordable, easy to use, and, importantly, they let you watch living cells.
Compound Light Microscope
A compound light microscope magnifies in two stages: an objective lens close to the specimen, then an eyepiece. Typical objectives are 4x, 10x, 40x and 100x, used with a 10x eyepiece, which gives totals of 40x to 1000x.
It’s used for thin, translucent specimens mounted on glass slides: cheek cells, onion epidermis, blood smears, protozoa, algae, stained bacteria and tissue sections. Light usually shines up through the specimen from below. Our step-by-step guide to how a compound microscope works follows that light path.
Stereo (Dissecting) Microscope
A stereo microscope has two separate optical paths, one for each eye, viewing the specimen from slightly different angles. This gives a genuinely three-dimensional view. Magnification is lower, often in the range of about 7x to 40x or so. In return you get a long working distance, so there’s room to handle the specimen with forceps or a dissecting needle.
Biologists use stereo microscopes for dissections, sorting insects, examining flowers and seeds, and picking out small organisms from samples. A binocular compound microscope is not a stereo microscope. It has two eyepieces, but both see the same image through one objective, so there’s no 3D effect.
Inverted Microscope
An inverted microscope puts the objectives below the stage and the light source above it. This lets you look up through the bottom of a flask or Petri dish at cells growing on the base. Inverted microscopes are standard in cell culture work, in vitro fertilization labs and live-cell imaging.
Contrast-Enhancing Light Microscopes
Many living cells are nearly transparent, so specialized light microscopes add contrast in different ways:
- Phase contrast turns tiny differences in how cells slow down light into visible light and dark differences. Widely used for unstained living cells.
- Darkfield blocks direct light so only light scattered by the specimen reaches the eye. Specimens appear bright against black.
- Differential interference contrast (DIC) gives a shaded, almost relief-like image of transparent specimens.
- Fluorescence uses fluorescent dyes or proteins that glow under specific wavelengths of light, so particular molecules or structures can be highlighted.
- Confocal is a fluorescence technique that uses a laser and a pinhole to reject out-of-focus light, producing sharp optical “slices” that can be stacked into 3D images.
Each of these is explained in our guide to the 7 types of light microscopes.
Types of Compound Light Microscope
“Compound light microscope” covers a wide range of instruments. They are usually grouped in a few different ways.
By viewing head:
- Monocular: One eyepiece. Simple and cheap, common in schools.
- Binocular: Two eyepieces for more comfortable viewing over long sessions.
- Trinocular: Two eyepieces plus a third port for a camera.
By configuration:
- Upright: The familiar layout, with objectives above the stage. Used for slides.
- Inverted: Objectives below the stage. Used for culture vessels.
By contrast method: Brightfield (standard), darkfield, phase contrast, DIC, polarizing and fluorescence. Many microscopes can be upgraded from brightfield to darkfield or phase contrast by changing the condenser and objectives.
By optical correction: Objectives are graded as achromat, semi-apochromat (fluorite) or apochromat, according to how well they correct color fringing. “Plan” versions also give a flat field of view.
Digital: Some compound microscopes have a built-in camera and screen, or connect to a computer. The optics underneath are still those of an ordinary compound microscope.
Electron Microscopes
Electron microscopes replace light with a beam of electrons, which has a much shorter wavelength. This allows far higher resolution, enough to see the internal structure of organelles, viruses and large molecules. The specimen usually sits in a vacuum and has to be carefully prepared, so it can’t be alive.
- Transmission electron microscope (TEM): Electrons pass through an ultra-thin slice of specimen. TEM gives detailed two-dimensional images of internal structure, such as membranes, ribosomes and the folds of mitochondria.
- Scanning electron microscope (SEM): A focused beam scans across the surface of a specimen, which is often coated with a thin layer of metal. SEM gives striking images of surfaces that look three-dimensional, such as pollen grains, insect eyes or bacteria on a surface.
- Cryo-electron microscopy (cryo-EM): Specimens are rapidly frozen so they’re preserved closer to their natural state. Cryo-EM is now widely used to work out the 3D shapes of proteins and other biological molecules.
Electron microscope images are naturally grayscale; colored versions have had false color added afterwards. See our comparison of light vs electron microscopes for the trade-offs.
Scanning Probe Microscopes
Scanning probe microscopes don’t use lenses at all. A very sharp tip on a flexible cantilever is moved across a surface, and its tiny movements are recorded to build a 3D map. In biology, the atomic force microscope (AFM) is the main example. It can image surfaces such as cell membranes, DNA and proteins at very high resolution, and some setups can work in liquid.
Comparison Table
| Type | Image formed by | Typical magnification | Live specimens? | Best for in biology |
|---|---|---|---|---|
| Compound light | Light through specimen | About 40x–1000x | Yes | Cells, tissues, microorganisms on slides |
| Stereo | Reflected or transmitted light, two optical paths | About 7x–40x+ | Yes | Dissection, insects, plant parts |
| Inverted | Light from above, objectives below | Usually 40x–400x | Yes | Cell cultures in dishes and flasks |
| Fluorescence / confocal | Light emitted by fluorescent labels | Similar to compound | Often | Locating specific molecules and structures |
| TEM | Electrons through thin section | Up to hundreds of thousands of times and beyond | No | Internal ultrastructure, viruses |
| SEM | Electrons scanned over surface | Very wide range, into the hundreds of thousands | No (in standard instruments) | Surface detail, 3D-looking images |
| AFM | Physical tip traced over surface | Not usually described by magnification | Sometimes | Surfaces and molecules at nanometer scale |
Magnification ranges are typical values and vary between instruments.
Why Lists of “16 Types” Vary
You’ll find articles listing 5, 7, 12 or 16 types of microscopes. They aren’t wrong so much as counting differently. Some lists treat every contrast method as a separate microscope. Some include industrial instruments such as metallurgical and comparison microscopes. Some count digital, USB and pocket microscopes as types of their own. The three-family grouping (light, electron, scanning probe) is the most useful starting point, because every other type fits inside it.
Which Type Should You Use?
For most biology students and home microscopists, the answer is a compound light microscope for slides and a stereo microscope for whole, solid specimens. Together they cover a remarkable range of subjects. Fluorescence, confocal and electron microscopes are usually found in research and clinical facilities, where specialist staff run them.
If you’re thinking of buying a microscope for home use, our guide to getting started with amateur microscopy explains how to choose between these two everyday types.