If the ice rings are really sharp, they trigger the bad background rejection in denzo/HKL2000. To reject more spots, increase the "reject fraction 0.7" parameter to something greater than .7. This rejection is on a spot by spot basis, so spots with good background between the rings should not be affected. During integration, if you are monitoring the process with Xdisp, you will see the rejected spots turn red and/or disappear. To verify they are being rejected by background fraction, try again with "reject fraction .3" and see if they stay green/yellow.
If the ice ring is broad compared to the integrating box, it shows up as a high, slanting baseline and the normal baseline correction procedure is valid, but sigma will be higher than for a spot on a white background. Francis E Reyes wrote:
All, So I have two intense ice rings where there appear to be lattice spots in between them. I understand that any reflections that lie directly on the ice ring are useless, however, how do software programs (HKL2000, d*Trek, mosflm, XDS) deal with these intermediate spots? It would seem to me that employing a 'resolution cut off' just before the ice ring (on the low resolution side) would be improper, as there are spots on the high resolution side of the ice. (see enclosed .tiff) In fact, how do these programs deal with spots lying on ice rings? Are they rejected by some algorithm by those programs during integration, or is it up to the scaling/merging (by SCALA for example) step to deal with them? Thanks! F --------------------------------------------- Francis E. Reyes M.Sc. 215 UCB University of Colorado at Boulder
