Hi
Marcus Mueller (from Dectris, who develop and manufacture the
Pilatus) did some work on this a couple of years ago and determined
that an oscillation angle ~ 0.5x the mosaicity of the crystal (using
the XDS value of mosaicity, which is not the same as Mosflm's); the
abstract says -
The results show that fine ’-slicing can substantially improve
scaling statistics and anomalous signal provided that the rotation
angle is comparable to half the crystal mosaicity.
Acta Cryst. (2012). D68, 42-56 [ doi:10.1107/S0907444911049833 ]
Optimal fine
-slicing for single-photon-counting pixel detectors
M. Mueller, M. Wang and C. Schulze-Briese
My reading of this is that there is still a place for strategy
calculations.
On 30 Apr 2014, at Wed30 Apr 15:06, Sanishvili, Ruslan wrote:
Hi Jacob,
I'll take a first crack as I am sure many will follow.
It is true that with CCD detectors one has to be careful how small
an oscillation range to use for a frame before read noise starts to
eat into the data quality.
Pilatus offers two major new features - is fast and is photon
counting as opposed to integrating detector.
The speed allows to collect data without a shutter and it is very
important as it can dramatically improve data quality. Now there
are fast CCD detectors as well on the market.
Being a photon counter, Pilatus has no "read" noise which, as you
have pointed out, allows you to collect as thin a frame as you
want. However, it is if you consider the detector only. In reality,
if you go very thin and very fast, you may not have enough flux to
record the data. Also, even once we get rid of the shutter, there
are still other sources of instabilities and they do affect the
fast data collection adversely. One could try going (very) thin
sliced and somewhat slow but there is another gotcha there. Most
rotation stages used for rotating the sample crystal, do not like
going extremely slow which would be the case with thin frames and
long exposure times. In this case the speed may not remain as
constant as we would like during data collection.
I think there was a publication from Diamond Synchrotron discussing
strategies of data collection with Pilatus.
We've done a little bit of systematic studies as well and while
things may well be sample- and facility-dependent, ~0.2 degree
frames with ~0.2 sec exposure time seemed to make good compromise
between above-mentioned issues. Here I would like to emphasize
again - there certainly will be samples which will benefit from
somewhat different parameters.
Hope it helps,
Cheers,
N.
Ruslan Sanishvili (Nukri)
Macromolecular Crystallographer
GM/CA@APS
X-ray Science Division, ANL
9700 S. Cass Ave.
Lemont, IL 60439
Tel: (630)252-0665
Fax: (630)252-0667
rsanishv...@anl.gov
________________________________________
From: CCP4 bulletin board [CCP4BB@jiscmail.ac.uk] on behalf of
Keller, Jacob [kell...@janelia.hhmi.org]
Sent: Wednesday, April 30, 2014 7:49 AM
To: CCP4BB@jiscmail.ac.uk
Subject: [ccp4bb] Pilatus and Strategy wrt Radiation Damage
Dear Pilatus/Radiation Damage Cognoscenti,
I read a few years ago, before the advent of Pilatus detectors,
that the best strategy was a sort of compromise between number of
images and detector readout noise "overhead." I have heard that
Pilatus detectors, however, have essentially no readout noise, so I
am wondering whether strategies have changed in light of this,
i.e., is the best practice now to collect as many images as
possible at lowest exposure possible?
JPK
*******************************************
Jacob Pearson Keller, PhD
Looger Lab/HHMI Janelia Farms Research Campus
19700 Helix Dr, Ashburn, VA 20147
email: kell...@janelia.hhmi.org
*******************************************
Harry
--
** note change of address **
Dr Harry Powell, MRC Laboratory of Molecular Biology, Francis Crick
Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0QH
Chairman of European Crystallographic Association SIG9
(Crystallographic Computing)
