Just to add to a comment on this, while global radiation damage is visually noticed in the tail off of high resolution reflections, all the reflections are impacted. It is best to collect the low resolution data first with much reduced exposure time, attenuated beam, and make use of the larger oscillation angle available. In the good old days there were special beamstops developed for this and a great example is provided by SSRL at http://smb.slac.stanford.edu/facilities/hardware/other/largebs.html. In this manner the low resolution data can be collected with the same dose as a single higher-resolution oscillation. The merging of reflection is also much easier this way round (we tried both ways).
I was able to collect 0.8A data on a >40KDa protein that involved a low, medium and high set with a little manipulation of energy to maximize space on the detector. That was a decade ago and the structure is still being refined - such is the richness of high-resolution. If something diffracts like this, pull the detector back and ignore the temptation ☺ Best, Eddie Shameless plug – http://getacrystal.org Edward Snell Ph.D. Biological Small Angle Scattering Theory and Practice, Eaton E. Lattman, Thomas D. Grant, and Edward H. Snell. Available through all good bookshops, or direct from Oxford University Press Director of the NSF BioXFEL Science and Technology Center President and CEO Hauptman-Woodward Medical Research Institute BioInnovations Chaired Professorship, University at Buffalo, SUNY 700 Ellicott Street, Buffalo, NY 14203-1102 hwi.buffalo.edu Phone: (716) 898 8631 Fax: (716) 898 8660 Skype: eddie.snell Email: [email protected] Webpage: https://hwi.buffalo.edu/scientist-directory/snell/ [cid:[email protected]] Heisenberg was probably here! From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Marc Graille Sent: Wednesday, October 10, 2018 11:14 AM To: [email protected] Subject: Re: [ccp4bb] Issue with high Rfree (0.25) for a high-resolution dataset (1.05 Ang) Dear Auto, with such crystals diffracting like rocks, it can be useful to collect two datasets. One at “low" resolution (up to 3A) using low exposure time and/or low dose to avoid overloads and a second at higher resolution (1A in your case) using higher dose. Then, merge those two datasets into a single one using all reflections from the “low resolution” dataset and for instance data from 5 to 1A for the high resolution data (to exclude overloads). It may improve the Rmeas values at low resolution. My two cents. Marc Marc GRAILLE, PhD Directeur de recherche CNRS Laboratoire de Biochimie ECOLE POLYTECHNIQUE - UMR7654 CNRS 91128 PALAISEAU CEDEX FRANCE ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
