Cameras rotation/oscillation

Of the many types of X-ray cameras, only two are still in even occasional use in protein crystallography — the Buerger or precession camera and the rotation/oscillation camera. The precession camera is used primarily in... 

Precession cameras are complex but give the diffraction pattern in its simplest, most understandable form. Rotation/oscillation cameras are far simpler, merely providing means to rotate the crystal about an axis perpendicular to... 

None of the data films happened to show the orthorhombic symmetry, thus a preliminary report specified the approximate cell constants for a primitive monoclinic cell P2i (Makowski et al 1987). Figure 10.26 shows the statistical distribution of approximate Bragg resolution found for the first film from each crystal, figure 10.27 displays the quick loss in resolution as a function of the exposure time/film number. In order to average out the resolution decay during each exposure, the camera rotation axis was oscillated ten times per photograph. 

Fig. 7.4. The rotation-oscillation (cylindrical) camera. Monochromatic Ka is used. The crystal shown at the center is rotated or oscillated. The layer lines formed by the intersection of diffraction cones and the cylindrical film are shown for different I values...

Only from 1985 onwards could we seriously consider crystallographic data collection. In fact, several full sets of oscillation films have since been exposed on the rotation camera however, they have tended to become outdated in view of new developments in the crystallization techniques or by other experimental improvements. 

The Laue method involves a stationary crystal and polychromatic ( white ) X rays. In the other camera methods, monochromatic radiation is used. In these cases the crystal may be oscillated over a small angular range (oscillation method) or rotated 360° about an axis (rotation method). The layer lines so formed may be selected individually. In the Weissenberg method, the oscillation of the crystal is coupled with a movement of the photographic film. The Buerger precession method, by a more complex motion of the instrument, produces an undistorted and magnified picture of the reciprocal lattice. 

The amplified signals from the crystals—the four gages were connected in parallel —were impressed on the horizontal-deflection plates of the cathode-ray tube. The screen of the tube was photographed with a rotating-drum camera. The drum ran at a uniform speed and, therefore, the time base was linear. Time calibration was obtained by means of a flashing neon crater tube (Sylvania, Type R1130B) which was activated by a 1000-cycle tuning-fork oscillator. The crater tube was in the... 

The present scanning speed is limited by the oscillating mirrors. The use of rotating polygon or acousto-optic scanners removes the limitation and a rotating polygon camera is soon to be developed for observing manipulator work. 

Weissenberg Camera. A camera for X-ray diffraction analysis of crystal structures. The crystal is rotated, in the X-ray beam. The film is rotated and moved parallel to the axis of rotation. Weissenberg Rheogoniometer. In essence a cone and plate viscometer (q.v.), but with accessories and control systems to allow it to measure, as well as viscosity, elasticity and a wide range of flow properties such as dilatancy, thixotrophy, relaxation phenomena, etc in steady rotation or in torsional oscillation, over wide but controlled ranges of temperature and shear. 

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