Main Types of Microscopes

The table below describes the main types of microscopes within the optical, electron, and scanning probe categories.

Optical microscope

Type Description
Digital microscope A microscopes that use a camera and magnified optics. It enables to output a live image to a monitor.
Binocular stereoscopic microscope A microscope that allows easy observation of 3D objects at low magnification.
Brightfield microscope A typical microscope that uses transmitted light to observe targets at high magnification.
Polarizing microscope A microscope that uses different light transmission characteristics of materials, such as crystalline structures, to produce an image.
Phase contrast microscope A microscope that visualizes minute surface irregularities by using light interference. It is commonly used to observe living cells without staining them.
What is a phase contrast microscope?

With a conventional biological microscope, it is difficult to observe colorless, transparent cells while they are alive. A phase contrast microscope makes it possible by utilizing two characteristics of light, diffraction and interference, to visualize specimens based on brightness differences (contrast).

Principle
With regard to periodic movements, such as sinusoidal waves, the phase represents the portion of the wave that has elapsed relative to the origin. Light is also an oscillation and the phase changes, when passing through an object, between the light that has passed through (diffracted light) and the remaining light (direct light). Even if the object is colorless and transparent, there is still a change in phase when light pass through it. This phase contrast is converted into brightness differences to observe specimens.
Features
  • Transparent cells can be observed without staining them because the phase contrast can be converted into brightness differences.
  • Because it is not necessary to stain cells, cell division and other processes can be observed in a living state.
Structure
Because diffracted light is too weak to be normally observed by the eye, a phase plate is located at the focal point of light between the objective lens and the image surface so that only the phase of the direct light changes. This generates contrast on the image surface.
Structural features include a ring aperture, instead of a pinhole, on the focal plane of the converging lens and a phase plate on the rear focal plane of the objective lens.
Differential interference contrast microscope This microscope, similar to the phase contrast, is used to observe minute surface irregularities but at a higher resolution. However, the use of polarized light limits the variety of observable specimen containers.
Fluorescence microscope A biological microscope that observes fluorescence emitted by samples by using special light sources such as mercury lamps. When combined with additional equipment, brightfield microscopes can also perform fluorescence imaging.
Total internal reflection fluorescence microscope A fluorescence microscope that uses an evanescent wave to only illuminate near the surface of a specimen. The region that is viewed is generally very thin compared to conventional microscopes. Observation is possible in molecular units due to reduced background light.
Laser microscope
(Laser scanning confocal microscope)
This microscope uses laser beams for clear observation of thick samples with different focal distances.
Multiphoton excitation microscope The use of multiple excitation lasers reduces damage to cells and allows high-resolution observation of deep areas. This type of microscope is used to observe nerve cells and blood flow in the brain.
Structured illumination microscope A high-resolution microscope with advanced technology to overcome limited resolution found in optical microscopes that is caused by the diffraction of light.
What is a structured illumination microscope?

A type of high-resolution microscope based on technology that has overcome the limited resolution of optical microscopes caused by the diffraction limit of light.

Principle
Conventionally, the resolution of optical microscopes was limited to 200 nm or larger due to the diffraction limit of light. This limit has been overcome by a high-resolution microscope developed in the United States that is based on structured illumination. Structured illumination microscopy enables high-resolution images to be obtained by using the moire effect of a grid or other patterned illumination (structured illumination) to capture diffracted light, which is impossible with conventional optical microscopes.
Features
  • Provides much higher resolution than conventional optical microscopes, approximately twofold, both in the horizontal and vertical directions.
  • Ability to process multiple captured images at high speed makes live imaging of cells possible.
Structure
Structured illumination microscopes do not have a new structure but use a new way to capture light. More specifically, this type of microscope is based on moire fringes, which are caused by interference of light, and is designed to emit a specific pattern of light (structured illumination) to generate moire effects. Because images captured through this technology contain detailed information about the object, high-resolution images can be composed through computerized analysis of multiple images.

Electron microscope

Type Description
Transmission electron microscope (TEM), scanning electron microscope (SEM), etc. These microscopes emit electron beams, not light beams, toward targets to magnify them.

Scanning probe microscope (SPM)

Type Description
Atomic force microscope (AFM), scanning near-field optical microscope (SNOM), etc. This microscope scans the surface of samples with a probe and this interaction is used to measure fine surface shapes or properties.

Others

Type Description
X-ray microscope, ultrasonic microscope, etc. -

In addition to the above categories, optical microscopes can be classified as follows:

Classification by application

Biological microscope With a magnification ranging from 50x to 1,500x, this microscope uses sliced samples that are fixed onto slides for observation.
(Binocular) stereoscopic microscope The binocular system allows 3D observation of samples, such as insects or minerals, in their natural state without the need to be sliced. The magnification ranges from 10x to 50x.

Classification by structure

Upright microscope Observes targets from above. This type of microscope is used to observe specimens on slides.
Inverted microscope Observes targets from below. This microscope is used to observe, for example, cells soaked with culture in a dish.

Magnified Observation and Instruments

A microscope is an optical instrument used to view small objects by enlarging them with two convex lenses. Optical microscopes, used for research, illuminate samples with visible or ultraviolet light. Depending on its structure, a biological microscope is categorized as an upright or inverted with a magnification ranging from 10x to 1500x.

Different types of microscopes are used based on the desired level of magnification. Magnifying glasses or loupes are used for quick inspection with a low magnification; binocular microscopes are used to observe from 10x to 50x, and upright/inverted microscopes are used to observe from 50x to 1500x.

Viewable objects by magnification

Magnification Instrument Example
1x Naked eye Hair (approx. 0.1 mm)
Approx. 2x to 5x Magnifying glass Plant or insect
Approx. 10x to 20x Stereoscopic microscope Water fleas and other microorganisms
Approx. 50x Upright/inverted microscope Insect's compound eye
Approx. 100x Upright/inverted microscope Paramecium
Approx. 200x Upright/inverted microscope Pollen
Approx. 400x Upright/inverted microscope Euglena
Approx. 800x to 1,500x Upright/inverted microscope Cell or chromosome
(approx. 0.2µm)
Approx. 2,000x to 1,000,000x Electron microscope Objects from 1μm to 0.1 nm such as a DNA (2 nm)

Trivia: What is the reference for a magnification of 1x?

A magnification of 1x is based on the point where a nearby object can clearly be observed by the human eye. Because this distance is 250 mm (distance of distinct vision), the size that can be observed at this distance is specified as 1x.

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