 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 4]](ba5199fig4mag.jpg)
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Figure 4
Crystal reorientation to avoid spot overlap owing to a long unit-cell axis oriented close to the beam: after the long axis (in this example c*, oriented in the plane of the loop) has been rotated into the plane perpendicular to the beam, the cell axis can be brought more parallel to the spindle axis by bending the loop in that plane. (a) Schematic representation of the goniometer showing the crystal in an arbitrary orientation, along with the laboratory reference frame conventions used by iMosflm. (b) Diffraction pattern and crystal view (upper inset) from the arbitrary crystal orientation, showing the close spacing of predictions characteristic of a long axis oriented close to the beam; strategy analysis in iMosflm indicates that data collection will be compromised by overlaps (not shown); it also provides (lower inset) the rotation required to bring the long axis into the iMosflm reference plane XZ (blue highlight). (c) Schematic showing the crystal rotated to place the long axis into the desired YZ plane: since it is perpendicular to the iMosflm reference plane, 90° is added to the angle indicated in (b). (d) Diffraction pattern of the rotated crystal, with the orientation of the long c* axis now clearly identifiable at 68° from the spindle axis; this angle needs to be reduced. (e) Schematic of how to reorient the crystal manually, using a sharp point to bend the loop in the required direction by pushing at where it is attached to the metal pin (care should be taken not to breathe away the cold stream!). Bending works best when pushing the nylon against the edge of the pin; the insert shows the less effective direction when bending towards the centre of the pin. Of course, a kappa goniometer, if present, allows the crystal to be tilted far more conveniently and accurately. (f) Diffraction pattern of the reoriented crystal, showing the long c* axis now significantly closer to the spindle axis, sufficient in this case to avoid spot overlap in the whole data set. |
![[Figure 4]](ba5199fig4.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
