LIGHT MICROSCOPY
Specimens are illuminated with light, which is focused using glass lenses and viewed using the eye or photographic film. Specimens can be living or dead, but often need to be stained with a coloured dye to make them visible. Many different stains are available that stain specific parts of the cell such as DNA, lipids, cytoskeleton, etc.
All light microscopes today are compound microscopes, which means they use several lenses to obtain high magnification. Light microscopy has a resolution of about 200 nm, which is good enough to see cells, but not the details of cell organelles. This limit is due to the wavelength of light (0.4-0.7 µm).
All light microscopes today are compound microscopes, which means they use several lenses to obtain high magnification. Light microscopy has a resolution of about 200 nm, which is good enough to see cells, but not the details of cell organelles. This limit is due to the wavelength of light (0.4-0.7 µm).
- The slide is placed on the stage and a light source (a light bulb or mirror in the base) directs the light upward
- Light passes through the specimen and through the objective lens, which is positioned directly above the specimen
- A set of objective lenses is located on the rotating nosepiece enlarges the image of the specimen with different powers of magnification
- From the objective lens, the magnified image is projected up through the body tube to the ocular lens in the eyepiece where it is magnified further (10X)
- To work out the total magnification of a microscope, multiply the power of magnification of the lens being used (40X, 100X) by the power of magnification of the ocular or eyepiece lens (10X) example: 40 X 10 = 400X total power of magnification
- The Resolution power of light microscopes is limited by the physical characteristics of light (At powers of magnification beyond about 2000X, the image of the specimen becomes blurred).