Types of Microscopes

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Types of Microscopes

Scanning

Uses a beam of electrons instead of light; electrons are reflected from the specimen; because of the shorter wavelength of electrons, structures smaller than 0.2 um can be resolved. The image produced appears three dimensional

To study the surface features of cells and viruses (usually magnified 100-100,000x)

Electron Transmission

Uses a beam of electrons instead of light, electrons pass through the specimen; because of the shorter wavelength of electrons, structures smaller than 0.2 um can be resolved. The image produced appears three dimensional.

To examine viruses or the internal ultra structure in thin sections of cells (usually magnified 10,000-100,000x)

Fluorescence

Uses an ultraviolet or near ultraviolet source of illumination that causes florescent compounds in a specimen to emit light.

For fluorescent antibody techniques rapidly detect and identify microbes in tissues or clinical specimens.

Phase-contrast

Uses a special condenser containing an annular (ring shaped) diaphragm. The diaphragm allows direct light to pass through the condenser, focusing light on the specimen and a diffracted light rays are brought together to produce the image. No staining required.

To facilitate detailed examination of the internal structures of living specimen.

Darkfield

Uses a special condenser with and opaque disk that blocks light from entering the objective lens, and the specimen appears light against a black background.

To examine living microorganisms that are invisible in bright field microscopy, do not stain easily, or are distorted by staining, frequently used to detect treponema pallidum in the diagnose of syphilis.

Light Bright field

Distinguishing Features: Uses visible light as a source of illumination; cannot resolve structures smaller than about 0.2 um; specimen appears against a bright background inexpensive and easy to use.

Principal Use: To observe various stained specimens and to count microbes; does not resolve very small specimens, such as viruses.