Fig. 2: Typical speckle images images collected by the three COLIS PCI cameras, where the number in the camera name designates the approximate scattering angle in air, and the SALS small angle camera, see text for the exact value of the scattering angles.

The PCI images have been cropped to show only the scattering volume; the bar corresponds to 1 mm. Different ROIs in the PCI images, such as the two boxes shown for PCI90, correspond to distinct regions of the scattering volume, but to the same scattering angle. For the SALS camera, each annular ROI corresponds to light scattered by the whole illuminated sample within a narrow range of scattering angles. The beam block that stops the transmitted beam is visible in the top-right corner, the cross indicates the position of the transmitted beam, and the blue bar corresponds to a scattering angle θ = 1°. Pixels masked by the beam block are excluded from the annular ROIs. See Section “Small-angle light scattering” for details on how the large variation of the scattered intensity with θ is dealt with, to avoid over- or under-exposing the image.