Microscopy is the study of objects too small to be visible to the naked eye. Different types of microscopes enable various levels of magnification and can be classified according to the way they create images from samples. Optical and electron microscopes are two main types of microscopes that use light and electron beams, respectively, to illuminate specimens.
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Optical microscopes, which include compound light microscopes, were the first to be invented and are the most common. In this type of microscopy, light from the microscope illuminates a specimen being examined. The maximum resolution of light microscopes is 200 nanometres when magnifying an object to view it at 1,000 times its actual size.
Compound Light Microscopes
Compound light microscopes are a type of optical microscope named for their multiple lenses. This type of microscope always has two or more lenses. Light passes through these lenses before reaching the eye, which magnifies the specimen. These microscopes tend to be bigger and heavier than simple microscopes, but can be used for more complex techniques.
Electron microscopes use beams of electrons, rather than light, to illuminate items being examined. Because the wavelength of an electron is much shorter than that of a photon -- the basic unit of light -- electron microscopes provide higher levels of magnification and resolution compared to compound light microscopes. Typical electron microscopes offer magnifications thousands of times higher than those of light microscopes and have resolutions that are hundreds of times higher.
Types of Electron Microscopes
Two types of electron microscopy are transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEMs pass electron beams through specimens, allowing the viewer to see structures within a specimen. SEMs are less powerful, providing less magnification, but are best for examining the surface of a material such as a metal up close. Basically, SEMs show topography of a sample, while TEMs show internal detail of a sample.
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