What is the resolution limit for an optical microscope?
In fact, the problem of the resolution limit of optical microscopes was solved by German physicist Abbe in 1873. Abbe discovered the limiting formula for the resolution of optical microscopes through calculation and derivation. The limit calculated by this formula is also called the Abbe limit.
The eyepieces and objective lenses used in optical microscopes are actually convex lenses. When light passes through the convex lenses, Airy disks are produced. A point we see through the microscope is actually a light spot. If the two points that need to be observed are relatively far apart, we can still distinguish them. But if these two points are very, very close, so close that the two Airy disks they produce overlap, then we can't tell whether they are two points, and we can only see blur. of a ball. Therefore, the size of the Airy disk actually determines the resolution limit of the microscope. Due to limited space, Tian Zongjun puts aside the derivation process here and gives a formula for the resolution of an optical microscope, as follows:
δ=0.61λ/(nSinα)
δ: Resolution λ: Wavelength n: Refractive index α: Aperture angle
After simple conversion, this formula is approximately equal to 1/2 λ, which means that one-half wavelength is actually the resolution limit of the optical microscope. Later generations defined it as the "Abbe limit".
The wavelength of violet light, the shortest wavelength in visible light, is about 400 nanometers, and the Abbe limit is about 200 nanometers. That is to say, if the distance between two points reaches less than 200 nanometers, the two points cannot be distinguished with an optical microscope. This is the resolution limit of the optical microscope.
