Tips and Tricks: Difference between revisions
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According to the classical paper ([http://dx.doi.org/10.1107/S0907444999008367 Z. Dauter (1999), Acta Cryst D55, 1703]), the required rotation range for native data in space group P1 is 180°, and for anomalous data is 180° + 2 theta_max (theta is the diffraction angle). In the case of the standard geometry (direct beam vertical to, and central upon, the detector), this leads to 2-fold redundancy. <br /> However, experience shows that collection of a few degrees more than that is a good idea, as the scaling will be more stable. So we regularly collect 200° for native data. <br /> The Pilatus 6M detector at the SLS is composed of many panels, and therefore has horizontal and vertical dead areas. This generally lowers completeness, and the effect is particularly noticeable in P1. Untested idea: it may be good to make sure (if necessary, by moving the Pilatus) that the direct beam is not at a crossing between horizontal and vertical dead areas, nor at the middle of a panel (because this avoids that equivalent reflections suffer the same fate). | According to the classical paper ([http://dx.doi.org/10.1107/S0907444999008367 Z. Dauter (1999), Acta Cryst D55, 1703]), the required rotation range for native data in space group P1 is 180°, and for anomalous data is 180° + 2 theta_max (theta is the diffraction angle). In the case of the standard geometry (direct beam vertical to, and central upon, the detector), this leads to 2-fold redundancy. <br /> However, experience shows that collection of a few degrees more than that is a good idea, as the scaling will be more stable. So we regularly collect 200° for native data. <br /> The Pilatus 6M detector at the SLS is composed of many panels, and therefore has horizontal and vertical dead areas. This generally lowers completeness, and the effect is particularly noticeable in P1. Untested idea: it may be good to make sure (if necessary, by moving the Pilatus) that the direct beam is not at a crossing between horizontal and vertical dead areas, nor at the middle of a panel (because this avoids that equivalent reflections suffer the same fate). | ||
== SAD/MAD data reduction == | |||
Run CORRECT twice, with STRICT_ABSORPTION_CORRECTION=TRUE and STRICT_ABSORPTION_CORRECTION=FALSE. I find that the anomalous signal in SeMet-SAD/MAD is significantly enhanced with STRICT_ABSORPTION_CORRECTION=TRUE (which used to be the default in older versions but ''currently is not the default''). | |||
Revision as of 23:47, 22 December 2007
P1 data collection / Pilatus
According to the classical paper (Z. Dauter (1999), Acta Cryst D55, 1703), the required rotation range for native data in space group P1 is 180°, and for anomalous data is 180° + 2 theta_max (theta is the diffraction angle). In the case of the standard geometry (direct beam vertical to, and central upon, the detector), this leads to 2-fold redundancy.
However, experience shows that collection of a few degrees more than that is a good idea, as the scaling will be more stable. So we regularly collect 200° for native data.
The Pilatus 6M detector at the SLS is composed of many panels, and therefore has horizontal and vertical dead areas. This generally lowers completeness, and the effect is particularly noticeable in P1. Untested idea: it may be good to make sure (if necessary, by moving the Pilatus) that the direct beam is not at a crossing between horizontal and vertical dead areas, nor at the middle of a panel (because this avoids that equivalent reflections suffer the same fate).
SAD/MAD data reduction
Run CORRECT twice, with STRICT_ABSORPTION_CORRECTION=TRUE and STRICT_ABSORPTION_CORRECTION=FALSE. I find that the anomalous signal in SeMet-SAD/MAD is significantly enhanced with STRICT_ABSORPTION_CORRECTION=TRUE (which used to be the default in older versions but currently is not the default).