SUMMARY
Diffraction occurs when light waves bend around the edges of an aperture, causing them to spread out. This phenomenon is not a lens aberration or a flaw in coatings, but a fundamental physical limit. The size and shape of the aperture determine the diffraction pattern, resulting in an Airy disc with a central bright spot and surrounding rings. At f/8, all lenses produce an identical 10.7-micron diffraction blur on the sensor, regardless of focal length or aperture diameter, because the f-number, not the physical aperture size, dictates the blur spot size on the sensor.
TAKEAWAYS
Diffraction is caused by light waves bending around an aperture, not by lens aberrations or reflections.
The Airy disc describes the diffraction pattern: a central bright spot surrounded by faint rings.
At f/8, all lenses produce the same 10.7-micron diffraction blur on the sensor.
The f-number, not the physical aperture diameter, determines the size of the diffraction blur on the sensor.