Microscope Observation Modes

Comparison among Observation Mode

A biological microscope uses transmitted light for observation. However, different observation modes have been developed to use specific light characteristics for specific samples, such as transparent specimens and samples that do not pass light.
The table below shows the features of major observation modes. Each observation mode has been developed to properly use characteristics of light such as scattering, diffraction, polarization, interference, and fluorescence.

Observation modes Features Common observation targets

A general observation mode for biological microscopes, which features a bright field-of-view with transmitted illumination

Living organisms, cells

Uses scattered light, not direct light, to make samples shine against a dark field-of-view

Microorganisms, cells

Uses phase (light variations) to convert a sample to brightness contrast for observation

Colorless transparent samples, living cells

Illuminates a sample with polarized light to convert it to brightness or color contrast for observation

Crystals such as rocks and minerals, polymers

Uses the difference in distances that the transmitted light travels after passing through a sample to generate color or brightness contrast for 3D observation

Colorless transparent samples, living cells

Converts the difference in heights of a sample to brightness contrast for 3D observation

Cells in plastic containers

Stains a sample with a fluorescent compound or fluorescent protein such as GFP to observe the part that expresses fluorescence

Cells and tissues dyed or labeled with a fluorescent dye, living organisms that exhibit intrinsic fluorescence

Uses reflected light to observe samples that do not pass light


Immerses a sample in index oil and uses transmitted light scattered in the oil for observation

Detection of asbestos

Features of Each Observation Mode

Brightfield microscopy

The type of microscopy generally used in biological microscopes. It illuminates the entire sample with direct light and observes it with transmitted or reflected light. This type of microscopy features a bright background and is widely used for inspection of dyed samples, pathologies, and semiconductors.

Darkfield microscopy

This type of microscopy only allows the light scattered or diffracted by the sample to enter the lens so that light can be projected against a dark field of view. It is suitable for observing colorless, transparent samples such as living cells, which are difficult to identify with brightfield microscopy. Darkfield microscopy also enables observation of minute features over the resolution limit of optical microscopes. A special condenser is used for this type of microscopy.

Phase contrast microscopy

This type of microscopy is based on the phase contrast (light variations) caused by light diffraction. Colorless, transparent samples, such as living tissues and cells, are difficult to image using brightfield, but they generate phase contrast due to their differing refractive indexes or thicknesses. Converting this contrast to brightness contrast enables this type of sample to be observed.
This type of microscopy allows cells and other objects that could only be observed against a dark field to be observed against a bright field. In addition, living specimens can be viewed because they need not be dyed. A ring-shaped phase plate with a slit in it needs to be used with this type of observation method.

Polarized light microscopy

Using polarization (biasing of vibration direction of light), this type of microscopy illuminates a sample and makes use of two polarizing plates that can be rotated for observation. If the plates are parallel, the sample appears bright; if the plates are perpendicular, the sample appears dark.
This type of microscopy is useful for observing rock and mineral slices to identify their crystal structures. It is also used to observe fibers, polymers, semiconductors, and bone tissues.
A special objective lens and two types of polarizing plates, polarizer and analyzer, are used for observation.

Differential interference contrast microscopy

As with phase contrast microscopy, differential interference contrast (DIC) microscopy is suitable for observing colorless, transparent samples. It differs in the imaging technique because DIC converts the difference in how light travels to changes in brightness, while phase contrast uses light diffraction.
It is suitable for observing relatively thick samples and also allows for 3D imaging. In addition, because images captured with this type of microscopy complements that captured with phase contrast microscopy, more accurate observation is possible by comparing the results of both.
Objective lenses are marked "DIC" if they are suitable for this type of microscopy.

Modulation contrast microscopy

Also called relief contrast microscopy, modulation contrast microscopy is suitable for observing colorless, transparent samples. Modulation contrast converts the difference in surface heights of a sample to brightness contrast for observation.
As with differential interference contrast, an image can be observed in 3D, although the principles differ. Another difference is that the use of plastic containers is allowed by modulation contrast microscopy, but not by differential interference contrast. Accordingly, this microscopy is suitable for observing sperm and egg cells.

Reflected light microscopy

This type of microscopy uses reflected light for observing samples that do not pass light, such as rocks and minerals. This category can also be further divided into subfields such as brightfield, darkfield, and differential interference.

Dispersion staining microscopy

By immersing a sample in index oil, dispersion staining microscopy performs observation by detecting light dispersions by the different refractive indexes of oil. It is mainly used to identify asbestos and their types.