Dear Sergei how much do the refined unit cell parameters (given a fixed detector distance) vary as a function of frame number? We have been using such initial diagnostic approach to trace radiation damage issues (among other problems) for a number of crystal forms that maximally diffracted in the 3.8-4.5 angstron range.
I copy/paste an excerpt from the XDS wiki that reinforces this approach: REFINE(INTEGRATE) The defaults (REFINE(INTEGRATE)=DISTANCE BEAM ORIENTATION CELL) could be modified by omitting DISTANCE, because one should assume that the distance is constant. This is particularly recommended if SPACE_GROUP_NUMBER=0 or 1. Furthermore, by fixing the distance one can better see from the results of the refinement whether the cell parameters are stable, or whether they change due to radiation damage. There are situations when one wants to reduce the number of parameters to be refined even more, see Optimization. Best regards Savvas ---- Savvas Savvides Unit for Structural Biology @ L-ProBE Ghent University K.L. Ledeganckstraat 35, 9000 Ghent, Belgium Ph. +32 (0)472 928 519 http://www.LProBE.ugent.be/xray.html On 05 Nov 2010, at 09:40, Sergei Strelkov wrote: > Dear All, > > I am processing a dataset collected (not by me) with 0.1 degree oscillations. > The diffraction is quite weak even though there is a clean diffraction > pattern to about 3A. > > Either Mosflm or XDS processes the data readily with +/- default settings > but both yield a high overall Rmerge of about 0.23 in the expected symmetry. > Processing in P1 yields an overall Rmerge of ~0.18, but what is especially > disappointing > is that Rmerge is as high as 0.15 at ~5A resolution already. > > The question is, how can we process the data so that the merging statistics > becomes more reasonable? > > Apparent mosaicity turns out to be ~0.5A. My naive way of thinking is > to try treating each five consecutive frames as a single 0.5 degree frame. > Does anyone have experience with this? > > Many thanks in advance, > Sergei
