Diffraction blur

Diffraction Blur: An optical softening of image details that occurs when light waves are forced through a tiny lens opening, causing them to bend and interfere with one another. While closing down your lens’s aperture (f-stop) normally increases depth of field, stopping down too far (like f/16 or f/22) triggers diffraction. Instead of focusing into a razor-sharp point on your sensor, the light spreads out into soft, overlapping circles (Airy disks), permanently degrading fine detail, text clarity, and film grain resolution across the entire frame.