Optical resolution & Airy disc calculator

Is your lens or your sensor the limit? Compare the diffraction spot of the aperture with the pixel size, and find the f-number where diffraction takes over.

Light
For white light, 550 nm (green, peak eye/sensor sensitivity) is the usual reference.
nm
Lens
×
0 for distant objects; e.g. 0.5 for close-up or macro work.
Sensor
µm
The Airy pattern drawn to scale over the pixel grid (rings brightened for visibility), its intensity profile against pixel boundaries, and Airy diameter versus f-number.

Details

    How it's calculated

    Even a perfect lens doesn't image a point as a point: diffraction at the aperture spreads it into a disc with rings, the Airy disc. Its diameter to the first dark ring depends only on wavelength λ and f-number N:

    Airy diameter = 2.44 · λ · N  ·  Rayleigh resolution = 1.22 · λ · N  ·  cutoff frequency = 1 / (λ · N)

    At close range (magnification m) the effective f-number N · (1 + m) applies. The sensor samples at its Nyquist frequency 1 / (2 · pixel size). As a rule of thumb, a system becomes diffraction-limited once the Airy disc grows beyond about two pixels — stopping down further still buys depth of field, but visibly costs sharpness.

    MTF at Nyquist is the contrast transfer of an ideal, aberration-free lens with a circular aperture. Real lenses fall below it (aberrations), so treat the value as an upper bound.

    All results are planning estimates based on simplified models and manufacturer data, without guarantee. Please verify critical values against the manufacturer datasheets before you make a design decision.

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