Microoscopes.txt

• Most widely used
• Forms its image when light is transmitted through the specimen
• The specimen produces an image that is darker than the surrounding illuminated field
• Can be used with live, unstained and preserved, stain specimens
• Visible Light

Used for live specimensSpecimen is contrasted against a gray backgroundExcellent for internal cell details Visible Light

• A bright-field microscope can be adapted to a dark-field microscope by adding a stop to the condenser
• The stop blocks all light from entering the objective lens except for peripheral light
• The specimen produces an image that is brightly illuminated against a dark field
• Effective for visualizing living cells that would be distorted by drying or heat or that can't be stained with usual methods
• Does not allow for visualization of fine internal details of cells
• Visible Light

• Allows for detailed view of live, unstained specimens
• Includes two prisms that add contrasting colors to the image
• The image is colorful and three-dimensionalUltraviolet rays are the source of illumination: (up to 2000X)
• Visible Light

• Includes a UV radiation source and a filter that protects the viewer's eyes
• Used with dyes that show fluorescence under UV rays
• Forms a colored image against a black field
• Used in diagnosing infections caused by specific bacteria, protozoa, and viruses using fluorescent antibodies
• Ultra violet Light

• Allows for viewing cells at higher magnifications using a laser beam of light to scan various depths in the specimen
• Most often used on fluorescently stained specimens
• Ultra violet Light

Originally developed for studying nonbiological materialsBiologists began using it in the early 1930sForms an image with a beam of electrons Electrons travel in wavelike patterns 1,000 times shorter than visible light wavesThis increases the resolving power tremendouslyMagnification can be extremely high (between 5,000X and 1,000,000X for biological specimens)Allows scientists to view the finest structure of cellsNote: Color can be added to the TEM & SEM images by computers

• Often used to view structures of cells and viruses
• Electrons are transmitted through the specimen
• The specimen must be very thin (20-100 nm thick) and stained to increase image contrast
• dark areas of a TEM image represent thicker or denser parts

• Creates an extremely detailed three-dimensional view of all kinds of objects
• Electrons bombard the surface of a whole metal-coated specimen
• Electrons deflected from the surface are picked up by a sophisticated detector
• The electron pattern is displayed as an image on a television screen
• Contours of specimens resolved with SEM are very revealing and surprising
• The images may be computer enhances to give them color