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
> [log in to unmask]
>
>
> ________________________________________
> From: CCP4 bulletin board [[log in to unmask]] on behalf of  
> Keller, Jacob [[log in to unmask]]
> Sent: Wednesday, April 30, 2014 7:49 AM
> To: [log in to unmask]
> 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: [log in to unmask]
> *******************************************

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)