Lens Diffraction Limit Calculator (Airy Disk vs Pixel Size)

How it works

Airy disk diameter = 2.44 × λ × N_eff (µm, λ in µm) · N_eff = N × (1 + magnification) · pixel pitch = sensor width ÷ horizontal pixels · diffraction-limited aperture ≈ 2 × pitch ÷ (2.44 λ) · effective MP ≈ MP ÷ (1 + (Airy ÷ 2 pitch)²)

Light passing through a circular aperture spreads into a diffraction pattern whose central bright spot — the Airy disk — grows in direct proportion to the f-number, because a smaller hole bends light more. Stopping down therefore sharpens a lens by hiding its aberrations only until the Airy disk becomes larger than the sensor can resolve; beyond that every point of the image is a blur disc wider than a couple of pixels and the extra megapixels record nothing new. High-resolution sensors with tiny pixels reach that point at wider apertures, which is why a 61-megapixel camera softens visibly by f/11 while a 12-megapixel one is fine at f/16. Macro photography is punished twice, since the effective aperture at life size is double the marked value.

Worked example

A 45 MP full-frame sensor has 8,216 × 5,477 pixels at a 4.38 µm pitch. At f/11 the Airy disk for green light is 2.44 × 0.55 × 11 = 14.8 µm — 3.4 pixels wide — so the image is clearly diffraction-limited, with an effective resolution around 12 MP. The diffraction-limited aperture is about f/6.5; landscapes are best shot at f/6.3–f/9 with focus stacking for depth.

Frequently asked questions