Re: [ccp4bb]: large cell

[Kay Diederichs <kay.diederichs@uni-konstanz.de>]

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Stefan Henrich wrote:
> 
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> Dear all,
> I have crystals in spacegroup P3 (maybe higher symm) with cell constants
> of about 136 A, 136 A, 475 A,  90.00  90.00 120.00 and unfortunately a
> mosaicity of about 0.6.
> I know that I need theoretically: deg(delta phi + mosaic) <= dmin (3.0
> A) / longest axis (475 A). This would mean (delta phi + mosaic) have to
> be less than 0.36 degrees instead of 0.7 (delta phi 0.1 + mosaic 0.6).
> Is there a strategy to overwhelm this problem?
> Thanks
> 
> Stefan

Stefan,

the worst case (the calculation you give above, except that it lacks a
factor of 180/3.14 as Dirk spotted) only applies when the long axis is
along the beam. Therefore the best strategy would be to align the
crystal so that the long axis is along the spindle. 
No matter what the crystal alignment is, during rotation the worst case
will not always apply. Whether you choose delta-phi of 0.1 or 0.2 won't
affect the overlap problem very much, but it _will_ affect the time your
data collection takes. 
Another factor that comes into play is that different programs (like
MOSFLM, denzo, xds) treat overlaps very differently. I have had good
experience with xds in terms of completeness in the face of high
mosaicity. You should try these programs yourself and test which gives
you the best data.

Kay
-- 
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