Uniform-disk spatial coherence
= Uniform-disk spatial coherence
For a monochromatic uniformly bright incoherent disk of angular diameter $\delta$, the mutual coherence at baseline $b$ is proportional to $2J_1(\pi\delta b/\lambda)/(\pi\delta b/\lambda)$. The first zero is $b\simeq1.22\lambda/\delta$. A nonuniform disk or finite spectral band changes the detailed curve.