Abstract: In the operation of a granulating or coating apparatus wherein a particulate material is processed in a granulation chamber into granules, the material may be photographed during the course of carrying out the granulation process by utilizing a photography probe wherein a bundle of optical fibers are utilized to project a source of stroboscopic illuminating light in the form of a generally flat beam through a portion of the granulating chamber and a photographic camera is focused within the projected light beam along an optical line of sight oriented generally perpendicular to the projected light beam to produce an image of granules within the beam against a relatively dark background.