Yes, a good summary. The use of the term redundancy (real or otherwise!) in crystallography is potentially misleading as the normal usages means superfluous/ surplus to requirements. The closest usage I can find from elsewhere is in information theory where it is applied for purposes of error detection when communicating over a noisy channel. Seems similar to the crystallographic use.
The more relevant point is what sort of errors would be mitigated by having different paths through the crystal. The obvious ones are absorption errors and errors in detector calibration. Inverse beam methods can mitigate these by ensuring the systematic errors are similar for the reflections being compared. However, my interpretation of the Acta D59 paper is that it is accepted that systematic errors are present and, by making multiple measurements under different conditions, the effect of these systematic errors will be minimised. Can anyone suggest other sources of error which would be mitigated by having different paths through the crystal. I don't think radiation damage (mentioned by several people) is one. Colin From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Frank von Delft Sent: 14 May 2013 14:23 To: ccp4bb Subject: [ccp4bb] Fwd: Re: [ccp4bb] reference for "true multiplicity"? George points out that the quote I referred to did not make it to the BB -- here we go, read below and learn, it is a most succinct summary. phx -------- Original Message -------- Subject: Re: [ccp4bb] reference for "true multiplicity"? Date: Tue, 14 May 2013 09:25:22 +0100 From: Frank von Delft <frank.vonde...@sgc.ox.ac.uk><mailto:%3cfrank.vonde...@sgc.ox.ac.uk%3e> To: George Sheldrick <gshe...@shelx.uni-ac.gwdg.de><mailto:gshe...@shelx.uni-ac.gwdg.de> Thanks! It's the Acta D59 p688 I was thinking of - start of discussion: "The results presented here show that it is possible to solve protein structures using the anomalous scattering from native S atoms measured on a laboratory instrument in a careful but relatively routine manner, provided that a sufficiently high real redundancy is obtained (ranging from 16 to 44 in these experiments). Real redundancy implies measurement of equivalent or identical re¯ections with different paths through the crystal, not just repeated measurements; this is expedited by high crystal symmetry and by the use of a three-circle (or ) goniometer." Wise words... phx On 14/05/2013 08:06, George Sheldrick wrote: Dear Frank, We did extensive testing of this approach at the beginning of this millenium - see Acta Cryst. D59 (2003) 393 and 688 - but never claimed that it was our idea. Best wishes, George On 05/14/2013 06:50 AM, Frank von Delft wrote: Hi, I'm meant to know this but I'm blanking, so I'll crowdsource instead: Anybody know a (the) reference where it was showed that the best SAD data is obtained by collecting multiple revolutions at different crystal offsets (kappa settings)? It's axiomatic now (I hope!), but I remember seeing someone actually show this. I thought Sheldrick early tweens, but PubMed is not being useful. (Oh dear, this will unleash references from the 60s, won't it.) phx -- This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail. Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom
