[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [ccp4bb]: dodgy indexing
*** For details on how to be removed from this list visit the ***
*** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
- I have seen patterns with similar problems at low resolution. I
wondered if it was due to the outer layers of a crystal becoming more
disordered than the bulk of the lattice during the cryoprotection
treatment. These outer layers might contribute more 'mosaic' reflections
and of course only diffract to lower resolution. The diffraction pattern
includes everything in the beam of course: good, bad, and ugly. I have
seen a similar effect with sample inhomogeneity in fibre diffraction. If
this is right then maybe you can cure the problem by improving the
treatment for cryoprotection.
On Tue, 27 Feb 2001, Jan Abendroth wrote:
> *** For details on how to be removed from this list visit the ***
> *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
> this reminds me my (large) crystal when I measured a high resolution
> data set at the synchrotron when we did not have enough time for the
> low-resolution scan. Although the final mosaicity from scalepack
> postrefinement was lower than the input in denzo: in the low resolution
> range not all spots were detected - the mosaicity seemed to be higher.
> The rest (autoindexing, chi^2, ... ) of the scaleing was very smooth.
> I made a compromize, taking a mosaicity slightly higher than the
> postrefined from scalepack for a second denzo-scalepack run. The
> data-set was fine anyway up to high resolution!
> I don't know exactly the resons for this behaviour. Maybe the crystal
> cracked a bit during freezing, or a small part of twinning (although
> merohedral twinning is not possible in this space group),...
> Maybe someone has made similar observations and knows a reason.
> Lauris Kemp wrote:
> > *** For details on how to be removed from this list visit the ***
> > *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
> > Hello
> > I'm trying to index a data set with denzo. The problem is with
> > mosaicity-it looks about 1 but at this value it misses out some low
> > resolution spots and seems to overfit for the number of spots at high
> > resolution. Thought it might be misindexed but did a direct beam shot
> > and the beam values look about right. It manages to autoindex it fine
> > and the chi values are also fine.
> > Lauris
> Jan Abendroth
> Institut fuer Biochemie
> Universitaet Koeln
> Zuelpicher Strasse 47
> D-50674 Koeln
> Tel: +49-(0)221 470 6455 (Labor)
> 6445 (Buero)
> Fax: +49-(0)221 470 5092