Abstract: A precession-type X-ray diffraction camera is provided with facilities for extending the range of information obtained by the crystal diffraction patterns on film without the necessity of additional handling of the crystal. The crystal holder is supported for movement within a circumferential groove of a circular segment that is attached to a support member carried in a two-axis mount. The circular segment is oriented in a plane that is perpendicular to such support member and which is parallel to an elongated element defining the axis of precession of the camera. The movement of the crystal holder in the groove permits an additional degree of variation of the crystal orientation with respect to the incoming collimated X-rays, without disturbing the nominal position of the crystal at the intersection of the collimation axis with the respective axes of the mount.