Yes of course; but the photons don't care what axis is being rotated
about, they kill just as rapidly.
George M. Sheldrick wrote:
> When discussing this issue, perhaps we should not lose sight of
> the fact that the statistics behind Rp.i.m. assume 'independent
> observations'. Surely doing more than one rotation about the
> same axis is likely to repeat the same systematic errors?
> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry,
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-22582
> On Tue, 9 Dec 2008, Frank von Delft wrote:
>> Hi Manfred
>>> thanks a lot for your comments, since they raise some interesting
>>> R_pim should give the precision of the averaged measurement,
>>> hence the name. It will decrease with increasing data redundancy,
>>> obviously. The decrease will be proportional to the square root
>>> of the redundancy if only statistical errors or counting errors
>>> are present. If other things happen, such as for instance
>>> radiation damage, then you are introducing systematic errors,
>>> which will lead to either R_pim decreasing less than it should,
>>> or R_pim even increasing.
>>> This raises an important issue. As more and more images keep
>>> being added to a data set, could one decide at some point,
>>> when to add any further images?
>> This really is the point: in these days of fast data collection, I assume
>> that most people collect more frames than necessary for completeness. At
>> least, I always do. So the question is no longer "is this data good enough"
>> -- that you can test quickly enough with downstream programs.
>> Rather, it is, "how many of the frames that I have should I include", so that
>> you don't have to run the same combination of downstream programs for 20
>> combinations of frames.
>> Radiation damage is the key, innit. Sure, I can pat myself on the shoulder by
>> downweighting everything by 1/1-N -- so after 15 revolutions of tetragonal
>> crystal that'll give a brilliant Rpim, but the crystal will be a cinder and
>> the data presumably crap.
>> But it's the intermediate zone (1-2x completeness) where I need help, but I
>> don't see how Rpim is discriminatory enough.