I think it is time to escalate that discussion to crystallographic definition 
purists like Massimo or to a logical consistency proponent like Ian who abhors 
definitional vacuum ūüėä  

 

Cheers, BR

 

From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Andreas Förster
Sent: Monday, June 29, 2020 15:24
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] number of frames to get a full dataset?

 

I like to think that the reflections I carefully measured at high multiplicity 
are not redundant, which the dictionary on my computer defines as "not or no 
longer needed or useful; superfluous" and the American Heritage Dictionary as 
"exceeding what is necessary or natural; superfluous" and "needlessly 
repetitive; verbose".

 

Please don't use the term Needless repetitivity in your Table 1.  It sends the 
wrong message.  Multiplicity is good.

 

All best.

 

 

Andreas

 

 

 

On Tue, Jun 30, 2020 at 12:03 AM James Holton <jmhol...@lbl.gov 
<mailto:jmhol...@lbl.gov> > wrote:

I have found that the use of "redundancy" vs "multiplicity" correlates very 
well with the speaker's favorite processing software.  The Denzo/HKL program 
scalepack outputs "redundancy", whereas scala/aimless and other more 
Europe-centric programs output "multiplicity".

At least it is not as bad as "intensity", which is so ambiguous as to be almost 
useless as a word on its own.

-James Holton
MAD Scientist

On 6/24/2020 10:27 AM, Bernhard Rupp wrote:

> Oh, and some of us prefer the word 'multiplicity' ;-0

Hmmm‚Ķmaybe not. ‚ÄėMultiplicity‚Äô in crystallography is context sensitive, and not 
uniquely defined. It can refer to 

a.      the position multiplicity (number of equivalent sites per unit cell, 
aka Wyckoff-Multiplicity), the only (!) cif use of multiplicity
b.      the multiplicity of the reflection, which means the superposition of 
reflections with the same d  (mostly powder diffraction) 
c.      the multiplicity of observations, aka redundancy.

While (a) and (b) are clearly defined, (c) is an arbitrary experimental number.

How from (a) real space symmetry follows (b) in reciprocal space (including the 
epsilon zones, another ‚Äėmultiplicity‚Äô) is explained here 

https://scripts.iucr.org/cgi-bin/paper?a14080 

and also on page 306 in BMC.

Too much multiplicity might create duplicity…   

Cheers, BR

 

Jon Cooper

 

On 23 Jun 2020 22:04, "Peat, Tom (Manufacturing, Parkville)" <tom.p...@csiro.au 
<mailto:tom.p...@csiro.au> > wrote:

I would just like to point out that for those of us who have worked too many 
times with P1 or P21 that even 360 degrees will not give you 'super' anomalous 
differences. 

I'm not a minimalist when it comes to data- redundancy is a good thing to have. 

cheers, tom 

 

Tom Peat
Proteins Group
Biomedical Program, CSIRO
343 Royal Parade
Parkville, VIC, 3052
+613 9662 7304
+614 57 539 419
tom.p...@csiro.au <mailto:tom.p...@csiro.au>  

 

  _____  

From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK <mailto:CCP4BB@JISCMAIL.AC.UK> 
> on behalf of 00000c2488af9525-dmarc-requ...@jiscmail.ac.uk 
<mailto:00000c2488af9525-dmarc-requ...@jiscmail.ac.uk>  
<00000c2488af9525-dmarc-requ...@jiscmail.ac.uk 
<mailto:00000c2488af9525-dmarc-requ...@jiscmail.ac.uk> >
Sent: Wednesday, June 24, 2020 1:10 AM
To: CCP4BB@JISCMAIL.AC.UK <mailto:CCP4BB@JISCMAIL.AC.UK>  
<CCP4BB@JISCMAIL.AC.UK <mailto:CCP4BB@JISCMAIL.AC.UK> >
Subject: Re: [ccp4bb] number of frames to get a full dataset? 

 

Someone told me there is a cubic space group where you can get away with 
something like 11 degrees of data. It would be interesting if that's correct. 
These minimum ranges for data collection rely on the crystal being 
pre-oriented, which is unheard-of these days, although they can help if someone 
is nagging you to get off the beam line or if your diffraction fades quickly. 
Going for 180 degrees always makes sense for a well-behaved crystal, or 360 
degrees if you want super anomalous differences. Hope this helps a bit. 

Jon Cooper

 

On 23 Jun 2020 07:29, Andreas Förster <andreas.foers...@dectris.com 
<mailto:andreas.foers...@dectris.com> > wrote:

Hi Murpholino,

 

in my opinion (*), the question is neither number of frames nor degrees.  The 
only thing that matters to your crystal is dose.  How many photons does your 
crystal take before it dies?  Consequently, the question to ask is How best to 
use photons.  Some people have done exactly that.

https://doi.org/10.1107/S2059798319003528


All best.

 

 

Andreas

 

 

(*) Disclaimer:  I benefit when you use PILATUS or EIGER - but I want you to 
use them to your advantage.

 

 

 

On Tue, Jun 23, 2020 at 12:04 AM Murpholino Peligro <murpholi...@gmail.com 
<mailto:murpholi...@gmail.com> > wrote:

Hi. 
Quick question...

I have seen *somewhere* that to get a 'full dataset we need to collect n 
frames':

at least 180 frames if symmetry is X

at least 90 frames if symmetry is Y

at least 45 frames if symmetry is Z

Can somebody point where is *somewhere*? 

 

...also...

what other factors can change n... besides symmetry and radiation damage?

 

Thanks

 

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