Diffraction Limit Aperture Calculator
Stopping down a lens increases depth of field, but past a point diffraction softens fine detail. Light passing through the aperture spreads into an Airy disk whose size grows with the f-number. This calculator computes the Airy disk diameter for your f-stop and light wavelength, then compares it to your sensor pixel pitch so you can see where diffraction begins to limit sharpness. Enter your f-number, the wavelength of light, and your pixel pitch.
Airy disk formula
Airy disk diameter d = 2.44 * lambda * N
lambda = wavelength, N = f-number
Softening begins when d > 2 * pixel pitch
The 2.44 factor gives the diameter from the centre to the first dark ring on both sides. When the disk exceeds about twice the pixel pitch (the Nyquist sampling limit) diffraction starts to visibly reduce resolution.
Worked example
At f/16 with 550 nm green light: d = 2.44 * 0.00055 mm * 16 = 0.02147 mm = 21.47 microns. For a sensor with 4.3 micron pixels, the ratio is 21.47 / 4.3 = 4.99, well above 2, so diffraction is clearly softening detail at this aperture.
Diffraction limit: frequently asked questions
What is the diffraction limit in photography?
Diffraction is the spreading of light as it passes through the lens aperture. The smaller the aperture (the higher the f-number), the larger the resulting blur spot, called the Airy disk. Beyond a certain f-stop the Airy disk grows larger than the detail your sensor can resolve, softening the image.
How is the Airy disk diameter calculated?
The diameter of the Airy disk (first dark ring to first dark ring) is 2.44 times the wavelength times the f-number: d = 2.44 * lambda * N. For green light at 550 nm and f/16, that is 2.44 * 0.00055 mm * 16 = 0.0215 mm.
When does diffraction start to soften my photos?
Diffraction becomes visible when the Airy disk diameter approaches twice the pixel pitch of your sensor (the Nyquist limit). This calculator compares the Airy disk to your pixel pitch so you can see the f-stop where softening sets in for your camera.
Sources
- NIST: Physical Measurement Laboratory (optical wavelength references).
- The Airy disk diameter d = 2.44 lambda N is the standard result for circular-aperture Fraunhofer diffraction.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.