Lens Diffraction Diaphragm mm

Diffraction limit by aperture (Airy disk)

The Airy disk diameter comes from d ≈ 1.22 · λ · N, where λ is given in micrometers (visible light sits around 0.55 µm) and N is the f-number. Run the numbers at f/16 and you get d ≈ 10 µm; at f/22 it's d ≈ 14 µm. Since the pixels on a modern camera measure only 4–5 µm, once you stop down past f/8–f/11 the disk already covers several pixels and the picture starts to go soft. That's the point where the lens becomes diffraction-limited.

Applications

Working out the practical resolution limit of a given sensor + lens combo, finding the maximum aperture before losing detail, knowing when to stack focus rather than stop down further in macro work, and weighing diffraction against depth of field in landscape photography.

FAQ

What is diffraction in photography? Light bends as it squeezes through a small opening. The tighter the aperture (the larger N), the more it spreads out, and that spreading is what blurs fine detail.

Why does f/22 look soft? At f/22 the Airy disk is about 14 µm, far bigger than any modern pixel, so the detail gets smeared across several pixels and averages away.

What is the best aperture for sharpness? On most sensors it lands around f/5.6–f/8, stopped down enough to clean up the aberrations you get wide open, yet still short of the diffraction limit.