Dear Mohamed,
In my experience, XDS handles high mosaicity very well and there is no reason to worry about the mosaicity as such. There are, however, two things you should check: (i) with high mosaicity you may get many overlaps resulting in many rejected reflections. If this is the case and you have incomplete data, you may try to fine-tune your processing. (ii) Why does the mosaicity suddenly goes up? Does the crystal go bad due to severe radiation damage? You can check in CORRECT.LP what the R-factors do during your run. If you have reasonable complete data after 1000 frames and the crystal becomes really bad afterwards, it might be better to discard the later frames.
Best,
Herman
-----Ursprüngliche Nachricht-----
Von: CCP4 bulletin board [mailto:[log in to unmask]] Im Auftrag von Mohamed Noor
Gesendet: Sonntag, 1. November 2015 17:36
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Betreff: [ccp4bb] Effect of high mosaicity (XDS)
Dear all
While processing my images, I notice that the first 1000 frames or so have a low mosaicity (0.3 degree) but this increases to about 2 degrees when all the 1800 frames (0.1 degree oscillation) are integrated.
At later stages of model building/refinement, what effect will a high mosaicity have? Should I just discard the images when mosaicity starts to increase?
I have fairly isomorphous datasets from about 10 more crystals with some exhibiting this behaviour and others do not. The point group seems to be P3 or P6, with some indication of twinning - not sure at this stage yet.
Thanks.
Mohamed
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