What is the theoretical limiting magnification of an optical microscope?
The resolving limit of an optical microscope is about 0.2 micrometers, which corresponds to a magnification of 1500 to 2000 times; to achieve greater magnification, an electron microscope or tunneling scanning microscope is used.
Magnifying lenses can refocus light to achieve magnification, using a combination of magnifying lenses to obtain optical microscopes; the limit of optical microscopes is limited by wavelength, and unlimited magnification is not possible.
Generally speaking, the resolution limit of optical microscope with fixed wavelength is half of the wavelength of light, and the wavelength of visible light is between 400~760nm, so the resolution limit of optical microscope is 200nm (0.2 micron). Objects smaller than 0.2 microns will not be resolved by an optical microscope, just as the tactile resolution of a human hand cannot exceed the small distance between tactile cells.
While magnification is a subjective statement, defined as the ratio of the size of an object seen by the human eye to its actual size at a distance of 25cm in plain sight, the 0.2 micron resolution of an optical microscope is equivalent to a magnification of 1500 to 2000 times, which is enough to allow us to see the structure of the average cell clearly.
If we use electromagnetic waves with shorter wavelengths, we can achieve greater magnification, but this is beyond the wavelength range of visible light; in 1931, the British physicist Luska invented the electron microscope, according to the principle of wave-particle duality, the electron beam has a shorter wavelength of the De Bruyne wave, so it can achieve a smaller resolution.
The accelerating voltage of the electron and its own wavelength corresponds to, when the voltage in 100 kilovolts, the wavelength of the electron beam is about 0.004nm (the actual resolution can only reach 0.2nm), is also much smaller than the wavelength of visible light, so the resolution limit of the electron microscope is far more than the optical microscope, the big one can realize the magnification rate of 3 million times, can distinguish the virus, the mitochondria, the DNA and other tiny objects.
