Protein Function Discovery
and Department of Biomedical and Molecular Sciences Molecular Modelling and Crystallographic Computing Facility 


Rough Calculation of Maximum DeltaPhi(oscillation angle for data collection)With longer cell axes, reflections that are in a line almost parallel with the Xray beam can become overlapped on one image as the crystal is rocked, if the oscillation angle is too large. The true maximum oscillation angle (deltaphi) depends on the orientation of the crystal because the longest cell axis may not be oriented in such a way that it affects the spacing of reflections in "phispace". After taking a single frame of data, the program strategy can be run to predict the optimum oscillation (phi) range and starting point, but it does not predict the maximum deltaphi. Mosflm on the other hand can calculate both the optimal oscillation starting point, range and angle. The optimum deltaphi can vary with the actual phi value (crystal orientation). For those that use HKL and strategy, I offer the following simple calculation.DeltaPhi is calculated using the formula: dphi = tan^{1}(res/cell)  mos, whereIn the case of the RAxes (sic), the vertical axis is actually horizontal. Last revised: Tuesday, 16Sep2003 10:34:49 EDT 