Tom makes a good point. The minimum RS coverage necessary to obtain a unique data set is just a simple calculation
that involves no experimental reality. To judge the expected usefulness of the data, you need to have some idea about the possible errors, random and systematic. Random is easy. Just collect longer (Poisson) and the counting error (precision) improves (sqrt(n)). Easy, would not radiation damage throw a wrench in into this concept, cf. all the threads by Holton, Elsbeth et al. Systematic, error, in absence of knowing the true value, becomes more interesting. One can average out some systematic errors by averaging multiple independent reflections (redundancy is rarely a bad thing, except for additional systematic error by overdoing exposure (as in hunt for highest resolution ) , but at least the mean will become more precise (not always, but often, more accurate too). Without advertisement for Dectris, collecting as much as you can (anomalously) as fast (lowest dose) as you can and sort out the stats later is a reasonable default in absence of other prior information. In his context, Id like to make a push for routine anomalous data, I was often surprised about the interpretative confirmation you can gain from a few clear anomalous peaks (or their absence). Best, BR From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Peat, Tom (Manufacturing, Parkville) Sent: Tuesday, June 23, 2020 14:04 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] number of frames to get a full dataset? 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 _____ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB <https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1> &A=1 -- Andreas Förster, Ph.D. Application Scientist Crystallography, Area Sales Manager Asia & Pacific Phone: +41 56 500 21 00 | Direct: +41 56 500 21 76 | Email: andreas.foers...@dectris.com <mailto:andreas.foers...@dectris.com> DECTRIS Ltd. | Taefernweg 1 | 5405 Baden-Daettwil | Switzerland | www.dectris.com <https://www.dectris.com> <https://www.dectris.com/files/content/images/signatur/logo_signatur.png> <https://www.linkedin.com/company/5067919> <https://www.facebook.com/pages/Dectris-Ltd/623855944369304> <https://twitter.com/DECTRIS_News> Confidentiality Note: This message is intended only for the use of the named recipient(s) and may contain confidential and/or privileged information. If you are not the intended recipient, please contact the sender and delete the message. 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