How does diffraction limit resolution?

Diffraction limits resolution by causing light waves to spread out and interfere with each other, reducing image sharpness.

Diffraction is a fundamental property of light, which behaves as both a particle and a wave. When light passes through a small opening or around an object, it spreads out and interferes with itself, creating a pattern of light and dark areas. This is known as diffraction. In imaging systems like microscopes, telescopes, and cameras, diffraction can limit the ability to distinguish between two closely spaced objects, which is known as resolution.

The resolution of an optical system is determined by the wavelength of light used and the size of the aperture through which the light passes. The smaller the aperture, the greater the diffraction and the lower the resolution. This is described by the Rayleigh criterion, which states that two points are just resolvable when the centre of the diffraction pattern of one is directly over the first minimum of the diffraction pattern of the other.

In other words, if the diffraction patterns of two points overlap too much, they cannot be distinguished from each other and appear as one blurred point. This is why images become less sharp and more blurry as you zoom in beyond the diffraction limit.

However, it's important to note that while diffraction limits the resolution, it doesn't mean that smaller details cannot be seen at all. Techniques such as super-resolution microscopy and the use of shorter wavelength light can help to overcome the diffraction limit and improve resolution.

In summary, diffraction is a fundamental property of light that can limit the resolution of an optical system. The smaller the aperture and the longer the wavelength of light, the greater the diffraction and the lower the resolution. However, techniques exist to overcome this limit and improve resolution.