Re: [ccp4bb]: Data reduction for mosaic crystals....

[Anastassis Perrakis <perrakis@nki.nl>]

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> Hi,
>
> Seems to me like a typical case where you should use XDS...
>
> Pete
>

..... well, it seems more like like a typical case of bad data collection
strategy ...  ;-)

> > Hi,
> > I am working on a dataset where the crystal hasy a very high mosaicity -
> > my
> > estimate is ~2.0 or more. Hence, I have had to take 0.1deg frames
> > during data
> > collection. Denzo V. 1.97.2 does not seem to be scaling the data very
> > well.

It is in general pointless to collect phi slices that are less than half the
mosaicity.

Why collect thin slices with high mosaicity ? Phine phi slicing gets really
powerfull with
low mosaicity crystals only! Typically people reduce the phi rotation in
order to avoid overlaps.
But, reducing it significantly lower than the mosaicty is pointless. ie. the
reflections will be overlapping
simply because they do overlap since they are much too 'wide' ... Thus, fine
slicing will not help
olving the problem and it will add very little to data quality when mosaicity
is high.

The best choice is to grow slightly different crystals, freeze them better,
or NOT freeze them
(people tend to forget that you can actually solve a structure without
cryo-freezing ...)

Steve Gamblin and Co had once good luck with VERY mosaic crystals in the
microfocus (>2.5), shooting just the edge
of the pillow-like crystal and I am told that this was the only thing that
worked for them. But try the simpler things first.

    Tassos

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