A device used in geology and crystallography as a technique of X-ray diffraction analysis.

In this technique, the X-ray beam is incident normal to the axis of rotation of the crystal and goniometer (another instrument, used for measuring the interfacial angles of crystal faces).

A cylinder of film, concentric with the rotation axis, oscillates through a large angle. Metal screens limit the diffracted beams to those from the zero layer of the reciprocal axis. The resulting picture can be used to calculate the lengths of crystallographic axes and the interaxial angles.
Multiple pictures can be taken, using different beam inclinations relative to the axis of rotation to study other lattice layers.