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Re: [ccp4bb]: A simple question of resolution
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Dear Robert,
the problem with questions about resolution is really that there
are many possible answers, and most of them mean something.
1. There is for instance the 'nominal resolution', which is usually
defined by some I/sigma(I) criterion. The consensus here seems
to be to use a value of 2.0 as the cutoff, provided that you have
observed at least 50% of all possible reflections in that shell.
2. A slightly better way may be to correct this nominal resolution
by the completeness of you data. Most data reduction programs don't
do that, but this is easy enough to do it yourself.
3. If you think of resolution in terms of 'how close can two features
in the electron density be that I can still resolve them' (which is
actually the true meaning of resolution), then you can resort too the
so-called 'optical resolution', which is described by Aleixei Vaguine
in Acta Cryst. D55, 191-205 (1999). Usually, the 'nominal resolution'
is a conservative estimate of the 'optical resolution', but the
'optical resolution' which you can calculate using the program
SFCHECK is certainly closer to the true resolution.
I hope that this answers your question. Some more discussion on that
you may also find in J. Appl. Cryst. 34, 130-135 (2001).
Cheers, Manfred.
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On Wed, 24 Apr 2002, Robert Lucas wrote:
> *** For details on how to be removed from this list visit the ***
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>
> Since this seems to be a ripe time for debates I figure I'll
> throw my fuel onto the fire...
>
> My question is a simple one, how do you determine what resolution
> to report your structure at?
>
> I'm not lucky enough enough to be in a situation with multiple complete
> MAD datasets that were solved used an ingenious program while I was
> drinking coffee. Instead I don't like coffee and my data is incomplete
> and gets quite sparse at high resolution.
>
> I'm interested in what is a proper method for reporting resolution in
> the worst/poor case scenarios, any references to papers on the topic
> would also be greatly appreciated.
>
> Thanks,
> Robert
>
>
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