Abstract: An interactive computer controlled asymmetric texture-sensitive parafocussing X-ray powder diffractometer employs an incremental rotating specimen device which permits azimuthal rotation (through the angle .phi. of the disc-shaped specimen about its surface normal. The rotating specimen device, rotatable about the principal diffractometer axis, can be offset an angle .alpha. from the symmetric position in which the specimen surface normal makes the angle (90-.theta.).degree. with both the source-to-specimen and detector-to-specimen directions. In order to maintain the Brentano focussing condition, the photon-counting detector is supported on a slide which is translated towards or away from the specimen by a stepper-motor drive lead screw. K, the ratio of the detector-to-specimen and x-ray source-to-specimen distances is constrained to the specified range c<K<f, where c is the smallest and f the largest ratio achieved. The focussing condition is realized by computer control which maintains K=sin (.theta.

Abstract: A diffractometer for acquiring crystallographic data from single crystal having means to mount the crystal in the path of a beam of x-rays, a moveable detector and means to constrain the detector to move on an arc which rotates about a horizontal axis so that the detector is sequentially positioned along a line of the reciprocal lattice of the crystal.