Microscope Types

For Microbiology

Brightfield illumination Compound Light Microscope

Dark objects are visible against a bright background

light reflected off the specimen DOES NOT enter the objective lens

Darkfield Microscopy

Light objects are visible against dark background

opaque disk placed in condenser

only light reflected off the specimen ENTERS the objective lens

Phase-Contrast Microscope

Allows examination of living organisms and internal cell structures

brings together two sets of light rays, direct reflected rays, and diffracted rays to form an image

Shows differentiation of internal structures and clearly shows the pellicle

Differential Interference Contrast (DIC)

Uses differences in refractive indexes

Uses two light beams and prisms to split light beams

Has contrast and color

nearly 3D image

Fluorescence Microscope

Uses UV (short wavelength) light

Fluorescent substance absorb UV light and emit longer wavelength (visible) light

Cells stained with dyes

Appears as bright objects against dark background

Confocal Microscope

cells are stained with dyes

short-wavelength (blue) light is used to excite a single plane of a specimen

each plane in a specimen is illuminated and a 3d image is constructed with a computer

Electron Microscope

Uses electrons instead of light

The shorter wavelength electrons gives greater resolution

Used for images too small to be seen with light microscopes, such as viruses, molecules and even individual atoms

Transmission Electron Microscopy

A beam of electrons passes through ultrathin sections of a specimen, then through an electromagnetic lens, then focused on a projector lens

Specimens may be stained with heavy-metal salts for contrast

Scanning Electron Microscopy

An electron gun produces a beam of electrons that scans the surface of an entire specimen

Secondary electrons emitted from the specimen produce a 3d image

Magnifies objects 1000 to 10,000x

Provides valuable topographical, morphological and compositional information of sample