Am 20:59, schrieb Harry Powell:
...
> I think there may be issues with collecting data too finely with a
> Pilatus, even in shutterless mode. I don't know where the problems arise
> (can't be shutter/rotation axis synchronisation), but it seems to be the
> normal thing in XDS (which should have no problems with fine
> phi-slicing) to use the "PATCH_SHUTTER_PROBLEM=TRUE" that Martin
> Hallberg suggested, which looks a bit like a fudge to me (but I expect
> Kay to correct me on that!).
...
Hi Harry,
no, it is a misunderstanding that the normal thing is to use
PATCH_SHUTTER_PROBLEM=TRUE in XDS; rather, it may be the last resort to
try before you abandon a dataset, and if the spindle/shutter
de-synchronization is so poor that this fudge needs to be used, then the
BL hardware needs to be fixed before other datasets are collected.
Two other points:
a) one may distinguish "weak data resulting in high R-factors" from
"problems with hardware or radiation damage resulting in high R-factors"
by looking at (I/sigma)^asymptotic as defined in Acta D66, 733 (
http://dx.doi.org/10.1107/S0907444910014836 ).
b) Marcus Müller (SLS) has shown (to me, unambiguously) that the best
data are obtained from the Pilatus if delta-phi is 1/2 to 1/4 of the
mosaicity (as reported by XDS). However, for the best data, other
parameters of the experiment (basically the transmission and the spindle
speed) have to be optimized as well. The finding of Tassos that 0.5-1
degree data gave the best result in a particular case might indicate
that these other factors of his experiment were not optimal (it is
indeed not trivial to get them right).
best,
Kay
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