Lens Diffraction Calculator
Optical and sensor inputs
Derived pixel pitch: 4.395 µm
Diffraction and sampling results
At these settings, the ideal diffraction cutoff is above the sensor Nyquist frequency. Pixel sampling reaches its theoretical limit first, although real image detail depends on the full optical and processing chain.
Advertisement
Airy disk by aperture
The current f-number is included with common full-stop values. Wavelength and pixel pitch follow the inputs above.
| Aperture | Airy diameter | Diameter in pixels | Diffraction cutoff | Cutoff ÷ Nyquist |
|---|---|---|---|---|
| Enter valid values to compare apertures. | ||||
How to use this lens diffraction calculator
- Enter the working aperture. Use the f-number set on the lens or reported by the camera.
- Choose a representative wavelength. Green 550 nm is a practical visible-light reference; use another wavelength for monochromatic or infrared work.
- Set the pixel pitch. Enter it directly, or calculate it from the active sensor width and horizontal pixel count.
- Enter focal length. Airy size at the sensor depends on f-number, not focal length, but focal length is needed for the entrance-pupil estimate and angular resolution.
- Compare scales, not pass/fail labels. The pixel and spatial-frequency results help explain sampling; they do not identify one universally “safe” aperture.
Formulas and assumptions
This calculator models monochromatic Fraunhofer diffraction from an ideal, unobstructed circular aperture. It uses the image-side working f-number and treats air as the medium.
Airy radius = 1.22 × λ × N
Diffraction cutoff = 1 ÷ (λ × N)
Sensor Nyquist = 1 ÷ (2 × pixel pitch)
Entrance pupil diameter = focal length ÷ N
Angular Rayleigh limit = 1.22 × λ ÷ entrance pupil diameter
Here, λ is wavelength and N is f-number. Airy diameter and radius use wavelength in micrometres to return micrometres. Spatial frequencies use millimetres and are shown as line pairs per millimetre, numerically equivalent to cycles per millimetre.
The Airy formula is documented by Edmund Optics. The angular Rayleigh criterion and first minimum at 1.22λ/D are described in NIST IR 8321.
How to interpret Airy disk and pixel-pitch results
Airy disk diameter is a physical scale, not a sharpness verdict
A point source passing through a circular aperture forms a bright central lobe surrounded by rings. The conventional Airy disk diameter runs between the first dark minima. As the lens is stopped down to a higher f-number, this diameter grows linearly. The point-spread function still transfers contrast at multiple spatial frequencies, so comparing the disk with one pixel is informative but not a binary quality threshold.
Pixel pitch describes sampling at the sensor
Smaller pixels place more samples in each millimetre. The Nyquist frequency shown here is the ideal limit for a uniformly sampled monochrome grid. Most colour cameras use a Bayer or other colour-filter array, and their channel response, optical low-pass filter, demosaicing, sharpening, and noise alter the practical result. The calculator therefore reports the physical ratio without claiming that one component alone controls final image resolution.
Wavelength changes the diffraction pattern
Blue light has a shorter wavelength and forms a smaller ideal Airy pattern than red or infrared light at the same f-number. Broadband photographs combine many wavelengths, while lens coatings, chromatic aberration, sensor spectral response, and raw processing contribute additional differences. Use a representative wavelength for planning and a wavelength-specific value for controlled illumination.
Real lenses can improve as you stop down—before diffraction dominates
Wide-open images may be limited more by spherical aberration, astigmatism, coma, field curvature, or focus error than by diffraction. Stopping down can suppress those aberrations even while the theoretical diffraction spot grows. The best working aperture is therefore a balance among lens behaviour, depth of field, shutter speed, noise, subject motion, and the output size—not simply the smallest calculated Airy disk.
Limits
This is an ideal optical model for planning and education. The calculated entrance pupil is the focal length divided by the f-number; it is not necessarily the physical iris opening. The model does not include measured lens MTF, aperture-blade shape, pupil magnification, macro effective f-number, atmospheric turbulence, sensor microlenses, colour-filter arrays, image stabilization, or post-processing. At high magnification, use the effective working f-number supplied by the optical setup rather than the marked infinity-focus f-number.
Lens diffraction FAQ
At what aperture does diffraction start?
Diffraction occurs at every aperture. It becomes more visible as the f-number rises and the Airy pattern grows, but there is no universal aperture where every camera suddenly becomes diffraction limited.
Should the Airy disk be smaller than one pixel?
Not necessarily. Pixel pitch is only one sampling measure, and an Airy pattern contains useful contrast beyond its central disk. A one-pixel comparison is a convenient scale marker, not a universal image-quality threshold.
Does sensor size change Airy disk diameter?
Not at the sensor plane when f-number and wavelength are fixed. Sensor size changes framing, enlargement, and often pixel pitch, which affect how the diffraction pattern is sampled and viewed.
Which wavelength should I use?
About 550 nm is a practical green-light reference for visible photography. Blue light produces a smaller theoretical Airy disk and red or infrared light produces a larger one. Real scenes contain a range of wavelengths.
Is diffraction cutoff the same as real lens resolution?
No. The cutoff is an ideal zero-contrast limit for a circular aperture. Aberrations, manufacturing tolerances, focus, motion, filters, sensor response, demosaicing, and processing reduce or reshape real image contrast.
How do I calculate pixel pitch from a sensor specification?
Divide the active sensor width in millimetres by the horizontal pixel count, then multiply by 1000 to convert millimetres to micrometres. Use active rather than nominal dimensions when available.
Does this calculator upload camera or lens settings?
No. Inputs and calculations stay in your browser and are not sent to a server.