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Circular Aperture Rayleigh Resolution

Estimate the small-angle diffraction limit from wavelength and an ideal circular aperture diameter.

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Enter the known values in the units shown. Results update as you type.
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At 500 nm wavelength, a 100 mm circular aperture gives a Rayleigh angle of 0.0000061 rad, approximately 1.258 arcseconds.

Rayleigh angle in radians ≈ 1.22 × wavelength / aperture diameter

Enter these known values and leave the other values blank.

Wavelength, diameter and resolution must be positive. Use wavelength in the relevant propagation medium.
The 1.22 factor is the conventional rounded circular-aperture Rayleigh coefficient. The expression uses the small-angle approximation and requires an aperture large compared with wavelength.
This estimates an ideal diffraction limit for an unobscured circular aperture. Atmospheric seeing, optical aberrations, sampling, obstruction and contrast can worsen practical resolution.

Yes, within this ideal model at fixed wavelength. A smaller limiting angle indicates finer angular resolution.

No. The coefficient is rounded and the model omits practical limits. Extra displayed digits only describe the arithmetic.

Bookify requires a positive wavelength as well as positive aperture diameter and angular resolution.