A microscope is a device that allows people to view specimens in detail too small for the naked eye to see. They do this by magnification and resolution. Magnification is how many times the object is enlarged within the viewing lens. Resolution is how detailed the object appears when viewed. Microscopes are especially useful in biology, where many biologist study organisms too small to see without help. They may use stereoscopes, compound microscopes, confocal microscopes, electron microscopes, or any of the specialized microscopes within each category. The specimen under observation determines the microscope needed.
The stereoscope, also called the dissecting microscope and stereo microscope is a light illuminated microscope that allows a three-dimensional view of a specimen. It does this by using two eyepieces at different angles which are really just a pair of compound microscopes. The image of the specimen is also lateral and upright. However, stereoscopes have lower power compared to compound microscopes. Images are only magnified up to about 100x. Stereoscopes allow students and scientists to manipulate specimens while under observation.
Like stereoscopes, compound microscopes are illuminated by light. They give a two dimensional view of a specimen under observation but can have magnifications between 40x and 400x, with more powerful versions up to 2000x. Although the magnification can be high, resolution is limited by the wavelength of light. Compound microscopes cannot view detail less than 200 nanometers apart. Regardless, compound microscopes can be found in many biology classrooms and research laboratories.
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Confocal microscopes are also light microscopes, but have the advantages of both stereoscopes and compound microscopes. Confocal microscopes allow high magnifications of specimens with three dimensional images. They also have higher resolutions, able to differentiate details down to 120 nanometers apart. The most common type of confocal microscope is the fluorescent microscope. This microscope uses intense light to excite the molecules of a specimen. These molecules give off light, or fluorescence which is observed, allowing for higher magnification and resolution.
Transmission Electron Microscope
The first electron microscope was a transmission electron microscope (TEM) invented in Germany in 1931 by Max Knoll and Ernst Ruska. It was created as a way to magnify objects more than what light microscopes were capable of. If light microscopes could magnify up to 1000x or 2000x at best, then the electron microscope could magnify objects to the 10,000x range. A TEM works by focusing a beam of single-energy electrons strong enough to pass through a very thin specimen. The resulting images are then viewed through electron diffraction or direct electron imagining.
Scanning Electron Microscope
There is discrepancy about how the SEM was invented, but it was created in the early 1930s. However, it wasn’t until 1965 that Cambridge Instrument Company marketed the first SEM. This was due to the complexity of the SEM’s scanning technology, which was more complicated to utilize than the TEM. The SEM works by scanning a sample’s surface with an electron beam. This beam creates different signals, secondary electrons, X-rays, photons, and others, which all help characterize the sample. The signals are displayed on a screen that maps out the sample’s material properties.