Low dose data: Difference between revisions

Low dose data (view source)

318 bytes removed , 4 June 2019

add DEFPIX "wrong detector parameters" workaround (thanks to Tim Grüne!)

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 This seems to work well down to an average of 0.05 counts/pixel. If, however, the crystal is exposed so shortly/weakly that the average drops significantly below this value, scaling becomes impossible - the ratio of averages which are around zero is obviously undefined. The keyword [http://homes.mpimf-heidelberg.mpg.de/~kabsch/xds/html_doc/xds_parameters.html#DATA_RANGE_FIXED_SCALE_FACTOR== DATA_RANGE_FIXED_SCALE_FACTOR] has been introduced to handle this situation.
-The following problem was fixed in the March 1, 2015 version of XDS: "Below 0.5 counts/pixel, the I/sigma values become overly optimistic. Data frames which have been collected too finely/weakly may be added together using the [http://homes.mpimf-heidelberg.mpg.de/~kabsch/xds/html_doc/merge2cbf_program.html merge2cbf] program of the XDS package. This is currently only relevant for the Pilatus and Eiger detectors; a typical low background on other types of detectors is more on the order of 10 counts/pixel (Holton and Fraenkel (2010) Acta Cryst. (2010). D66, 393–408; [http://dx.doi.org/10.1107/S0907444910007262])."
+Even if this feature is used, DEFPIX may stop with the (misleading) error message <pre>!!! ERROR !!! WRONG DETECTOR PARAMETERS</pre> If this happens, omit DEFPIX from the JOB= list of parameters, and copy BKGINIT.cbf to BKGPIX.cbf (DEFPIX would have to write BKGPIX.cbf, but this has to be done manually).
 See also: [[Difficult datasets]]