Jacob,

If you fine slice and everything is then a partial, isn't that *more* sensitive 
to lack of synchronization between the shutter and rotation axis than the 
wide-frame method where there's a larger proportion of fulls that don't 
approach the frame edges (in rotation space) ?  Especially if you're 3D profile 
fitting ?

Is fine slicing more or less beneficial at high resolutions relative to lower 
ones ?

Phil Jeffrey
Princeton
________________________________
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Keller, Jacob 
[kell...@janelia.hhmi.org]
Sent: Wednesday, November 30, 2016 5:44 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Effects of Multiplicity and Fine Phi with Equivalent 
Count Numbers

If the mosaicity is, say, 0.5 deg, and one is measuring 1 deg frames, about 
half the time is spent measuring non-spot background noise under spots in phi, 
which is all lumped into the intensity measurement. Fine slicing reduces this. 
But I am conjecturing that there is also fine-slicing-mediated improvement due 
to averaging out things like shutter jitter, which would also be averaged out 
through plain ol’ multiplicity.

I guess a third equal-count dataset would be useful as well: one sweep with 
six-fold finer slicing. So it would be:

One sweep, 0.6 deg, 60s
Six sweeps, 0.6 deg, 10s
One sweep, 0.1 deg, 10s

Or something roughly similar. Who will arrange the bets?

JPK


From: Boaz Shaanan [mailto:bshaa...@bgu.ac.il]
Sent: Wednesday, November 30, 2016 5:19 PM
To: Keller, Jacob <kell...@janelia.hhmi.org>; CCP4BB@JISCMAIL.AC.UK
Subject: RE: Effects of Multiplicity and Fine Phi with Equivalent Count Numbers

Hi Jacob,

I may have missed completely your point but as far as my memory goes, the main 
argument in favour of fine slicing has always been reduction of the noise 
arising from incoherent scattering, which in the old days arose from the 
capillary, solvent, air, you name it. The noise reduction in fine slicing is 
achieved by shortening the exposure time per frame. This argument still holds 
today although the sources of incoherent scattering could be different. Of 
course, there are other reasons to go for fine slicing such as long axes and 
others. In any case it's the recommended method these days, and for good 
reasons, isn't it?

  Best regards,

                   Boaz

Boaz Shaanan, Ph.D.
Dept. of Life Sciences
Ben-Gurion University of the Negev
Beer-Sheva 84105
Israel

E-mail: bshaa...@bgu.ac.il<mailto:bshaa...@bgu.ac.il>
Phone: 972-8-647-2220  Skype: boaz.shaanan
Fax:   972-8-647-2992 or 972-8-646-1710



________________________________
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Keller, Jacob 
[kell...@janelia.hhmi.org]
Sent: Wednesday, November 30, 2016 11:37 PM
To: CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>
Subject: [ccp4bb] Effects of Multiplicity and Fine Phi with Equivalent Count 
Numbers
Dear Crystallographers,

I am curious whether the observed effects of fine phi slicing might in part or 
in toto be due to simply higher “pseudo-multiplicity.” In other words, under 
normal experimental conditions, does simply increasing the number of 
measurements increase the signal and improve precision, even with the same 
number of total counts in the dataset?

As such, I am looking for a paper which, like Pflugrath’s 1999 paper, compares 
two data sets with equivalent total counts but, in this case, different 
multiplicities. For example, is a single sweep with 0.5 degree 60s exposures 
empirically, in real practice, equivalent statistically to six passes with 0.5 
degree 10s frames? Better? Worse? Our home source has been donated away to 
Connecticut, so I can’t do this experiment myself anymore.

All the best,

Jacob Keller


*******************************************
Jacob Pearson Keller, PhD
Research Scientist
HHMI Janelia Research Campus / Looger lab
Phone: (571)209-4000 x3159
Email: kell...@janelia.hhmi.org<mailto:kell...@janelia.hhmi.org>
*******************************************

Reply via email to