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Microscopy

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Microscopy is any of a number of techniques that use instruments which produce images of objects too small to be seen with the naked eye. Microscopy is typically used in microbiology and cell biology, but also in the investigation of the microstructures of metal or other materials. Using microscopic techniques, the intelligent design inherent within the created world becomes clearly evident.

The word microscope comes from the Greek words micros meaning "small" and scopoo which means "I am watching".

Microscope

Optical

Compound Optical Microscope
Optical microscope image of onion cells - 100X magnification

Compound optical microscopes can magnify an image up to 1000X, but have a very limited depth of field. Therefore, they are typically used to examine smears, squashed preparations, or a thinly sectioned slice of some material. An optical microscope involves passing light through a series of lenses, to be detected directly by the eye, captured in a photograph, or projected on a screen. The maximum resolution that one can image is determined by the wavelength of the photons that are being used to probe the sample; nothing smaller than the wavelength being used can be resolved. Visible light has wavelengths of 400-700 nanometers; larger than many objects of interest.

Typically, on a standard compound optical microscope, there are three objective lenses: a scanning lens (4X), a low power lens (10X), and high power lens (40X). Advanced microscopes often have a fourth objective lens, called an oil immersion lens that involves placing a drop of oil on the cover slip, and then immersing the objective in the oil. An oil immersion lens usually has a power of 100X. The actual power or magnification is the product of the powers of the ocular (eyepiece) or projection lens, usually about 10X, and the objective lens being used.

Electron

Main Article: Electron microscope
Scanning Electron Microscope
SEM image of the Rust Mite (Aceria anthocoptes) - magnified 1,400X.

An electron microscope is an electron-optical instrument in which a beam of electrons is used to produce an enlarged image of a minute object on a fluorescent screen or photographic plate. Electron microscopy is used when items or features are too small to be imaged by light. In this case, the image is created by the bending/reflection of an electron beam. Electron microscopy can magnify very small details with high resolving magnifying at levels up to 500,000 times.

  • Scanning Electron Microscope (SEM) - works by bombarding the object with the primary electron beam and then measuring the angles and energies of the secondary electrons scattered by the atoms on the surface of the object. It is used to produce images with a characteristic three-dimensional quality. The method is for determining the surface structure of a solid by measuring the angle and energies of electrons scattered by the atoms on the surface of a sample.
  • Transmission Electron Microscope (TEM) - works much like the light microscope, but generates in image by sending an electron beam through a very thin slice of the specimen. The resolution limit is around 0.05 nanometer.
  • Reflection Electron Microscope (REM) - sends an electron beam through the specimen but then uses the reflected beam of elastically scattered electrons to produce the image.
  • Scanning Transmission Electron Microscope (STEM) - bombards a very thin slice of material with electrons and then forms its image from secondary electrons scattered from this thin slice. This method can achieve resolutions comparable to that of TEM while producing three-dimensional images.

History of Microscopy

Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia (1655), which is the origin of the word "cell"

The origin of the microscope is a matter of debate, but many give credit to the Dutch spectacle-maker Zacharias Janssen for inventing the first compound microscope in the late 1500s. Galileo Galilei further improved upon the technology in the year 1609, by designing one with a convex and concave lens. The phase contrast and electron microscopes were both first invented in the 1930s. The phase contrast microscope was developed by the Dutch physicist Frits Zernike for which he was awarded the Nobel Prize in 1953. The first transmission electron microscope was built by Ernst Ruska.[1]

References

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