Circular-aperture diffraction and resolution criterion
A uniform ideal circular pupil of diameter D gives an Airy intensity pattern whose first dark ring has small angle θ≈1.22λ/D.
Key knowledge
A uniform ideal circular pupil of diameter D gives an Airy intensity pattern whose first dark ring has small angle θ≈1.22λ/D. The Rayleigh criterion places one incoherent point source's peak at the other's first minimum; microscope scale uses numerical aperture NA=n sinα and corresponding ideal lateral separation about 0.61λ₀/NA.
Values and equations
θ_R≈1.22λ/D; NA=n sinα; δ_R≈0.61λ₀/NA
- θ_R,α
- Resolution and collection half angles rad
- λ,D,δ_R,λ₀
- Medium wavelength, diameter, lateral separation and vacuum wavelength m
- n,NA
- Refractive index and numerical aperture
Conditions and scope
- Monochromatic scalar diffraction, unaberrated uniformly filled circular pupil, small angle for λ/D formula; λ₀ is vacuum wavelength in the NA expression.
- Rayleigh is a stated conventional resolution criterion, not a universal information-theoretic impossibility. Coherence, aberrations, signal-to-noise, sampling and estimation method affect actual distinguishability.
Sources · 1
References
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Evidence and review
University Physics 3: 4-5-circular-apertures-and-resolution: Equation 4.5, Rayleigh geometry and numerical-aperture paragraphs; replaces unqualified inescapable-resolution claims with criterion-specific scope.
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Entry details
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