Deviation angle
= Deviation angle
{title2=$\delta$}
The <angle> through which an optical element changes a <light ray>'s propagation direction, with the chosen branch and convention specified. For the one-internal-reflection branch through a spherical drop, entry <refraction>, internal <specular reflection>, and exit <refraction> give $\delta=\pi+2\alpha-4\beta$, with $\sin\alpha=n\sin\beta$. The corresponding primary <rainbow> radius about the antisolar direction is $\pi-\delta$.