The resolution of the precession camera

Transformations equations between reciprocal space and X-ray film are derived. With the use of these equations `resolution curves' representing the instrument resolution of a Buerger's precession camera can be defined. A point on the X-ray photographic film taken by the precession camera is proved to correspond to two resolution curves in the shape of the character `X' in reciprocal space. As an example, equi-intensity contours of thermal diffuse scattering from NaCl on an X-ray film were calculated on the basis of known elastic constant data, taking account of the resolution of the camera, and were compared with those in reciprocal space. Equi-intensity contours were found to be deformed considerably due to instrument resolution, unless the width of the layer-line screen was greatly reduced.