In general, if the Rmeas or Rmerge is high in the low resolution shells, then something is not optimal with the data collection.
Bill Shepard has already mentioned the loop vibrating or moving in the cryogenic gas flow. Other problems could be the goniometer head was loose, the magnet was loose, the pin was loose, etc. There could be excessive shutter shutter. The shutter and the crystal rotation could be poorly synchronized. There could be some other vibration in the system which could cause the X-ray flux to vary quite a bit. It could be as simple as the cycling of the cooling for the monochromator, the room or hutch, or the X-ray source itself. All of these would affect non-thin-images as wells. As already mentioned, combining thin-images into wider images will not overcome these problems. If Rmerge or Rmeas was 40% or more in the low resolution shells, then the diffraction pattern is probably mis-indexed, but that kind of high value was not reported here. OTOH, if "The diffraction is quite weak", one may be limited by counting statistics. This also cannot be overcome by processing. Jim -----Original Message----- From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of Sergei Strelkov Sent: Friday, November 05, 2010 3:41 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] High Rmerge with thin frames Dear All, I am processing a dataset collected (not by me) with 0.1 degree oscillations. The diffraction is quite weak even though there is a clean diffraction pattern to about 3A. ...
