Imaging scatterometry of butterfly wing scales

We describe an imaging scatterometer allowing hemispherical reflectance measurements as a function of the angle of incidence. The heart of the scatterometer is an ellipsoidal reflector, which compresses the hemispherical reflection into a cone-shaped beam that can be imaged by a normal optical system. The instrument's performance is illustrated by measurements of the scattering profiles of the blue-iridescent dorsal wing scales of the nymphalid Morpho aega and the matte-green ventral wing scales of the lycaenid Callophrys rubi.