What is the difference between a light microscope and an electron microscope?
1,Different imaging principles
The basic principle of optical microscope is to use the different structures of the sample to be examined to absorb the different characteristics of light, in the form of brightness difference presents the sample object image. In the electron microscope, the use of fine focusing electron beam in the sample surface point by point scanning, and sample interaction with the production of a variety of physical signals, these signals are received by the detector, amplification and converted into modulated signals, and finally in the fluorescent screen display reflecting a variety of characteristics of the sample surface image.
2, different illumination sources
The illumination source of the optical microscope is visible light (daylight or light), while the illumination source used in the electron microscope is the electron flow from the electron gun, due to the wavelength of the electron flow is much shorter than the wavelength of light waves, so the magnification of the electron microscope and the resolution of significantly higher than the light microscope.
HITACHI transmission electron microscope HT7800-Hitachi Atomic Force Microscope_Electron Microscope_Differential Scanning Calorimeter_Thermogravimetric Analyser_Spectrophotometer
3,Different lenses
Electron microscope plays a role in magnifying the objective lens is electromagnetic lens (can produce a magnetic field in the central part of the toroidal electromagnetic coil), while the objective lens of the optical microscope is a glass milled from the optical lens. There are three sets of electromagnetic lenses in the electron microscope, which are comparable to the functions of the focusing lens, objective lens and eyepiece in the optical microscope.
4, depth of field
The general depth of field of optical microscope is between 2-3um, so the surface smoothness of the sample has very high requirements, so the sample making process is relatively complex. Scanning electron microscope depth of field can be as high as a few millimetres, so there is no requirement for the geometry of the sample surface smoothness, sample preparation is relatively simple, and some samples do not require sample preparation. Although the body microscope also has a relatively large depth of field, but its resolution is very low.
5, the specimens used in different ways of preparation
Electron microscope observation of tissue cell specimens used in the preparation of more complex procedures, technical difficulties and costs are higher, in the sampling, fixation, dehydration and embedding and other aspects of the need for special reagents and operations, but also need to be embedded in a good block of tissue put into ultra-thin slicer cut into ultra-thin slices of 50 ~ 100nm thick specimen. The specimens for light microscopic observation are generally placed on slides, such as ordinary tissue section specimens, cell smear specimens, tissue compression specimens and cell drop specimens.
6, resolution
Optical microscope because of the interference and diffraction of light, the resolution can only be limited to between 2-5 um. The resolution of electron microscope can reach 1-3nm because it adopts electron beam as the light source. Therefore, the tissue observation of light microscope belongs to micron-level analysis, while that of electron microscope belongs to nanometer-level analysis.
7,Application field
Optical microscope is mainly used for micron-level tissue observation and measurement of smooth surfaces, because the use of visible light as a light source, so not only can observe the surface layer of the sample tissue and a certain range of tissues below the surface layer can also be observed, and optical microscope for the identification of colour is very sensitive and accurate. Electron microscopy is mainly used for nanometer scale observation of the surface morphology of the sample, because the scanning electron microscope relies on the intensity of the physical signal to distinguish the tissue information, so the scanning electron microscope image is black and white, for the recognition of colour images scanning electron microscope seems to be unable to help.
