What is the theoretical limit magnification of an optical microscope?

- Jul 09, 2019-

The resolution limit of optical microscopy is about 0.2 micron, which is equivalent to the magnification of 1500-2000 times. To achieve a larger magnification, an electron microscope or a tunnel scanning microscopemust be used.

The magnifier can refocus the light and achieve the magnification effect. The optical microscope can be obtained by using the combination of magnifiers. The limit of the optical microscope is limited by the wavelength and can not be enlarged indefinitely.

What is the theoretical limit magnification of an optical microscope?

Generally, the resolution limit of a fixed wavelength optical microscope is half of the wavelength of light, and the visible wavelength is between 400 and 760 nm, so the resolution limit of an optical microscope is 200 nm (0.2 micron). For objects less than 0.2 microns, the optical microscope will not be able to distinguish them, just as the tactile resolution of the human hand can not exceed the minimum distance between the tactile cells.

The magnification factor is subjective. It is defined as the ratio of the size of the object to the actual size when the distance between the eyes is 25 cm. The resolution of the optical microscope is 0.2 micron, which is equivalent to the magnification of 1500-2000 times. This is enough for us to see the structure of ordinary cells.

If we use shorter wavelengths of electromagnetic waves, we can achieve greater magnification, but this is beyond the wavelength range of visible light; in 1931, Lucas, a British physicist, invented the electron microscope. According to the principle of wave-particle duality, the electron beam has shorter DeBroglie wave wavelength, so it can achieve smaller. Resolution.

The acceleration voltage of the electron corresponds to its own wavelength. When the voltage is 100 KV, the wavelength of the electron beam is about 0.004 nm (the actual resolution can only reach 0.2 nm), which is also far less than the wavelength of the visible light. Therefore, the resolution limit of the electron microscope is much higher than that of the optical microscope, which can achieve a maximum magnification of 3 million times and can be distinguished. Viruses, mitochondria, DNA and other small objects.