Just to fill a little bit of the silence…

I agree that, in principle, with a detector with zero readout noise, there should be no penalty for spreading the photons over more frames.  My understanding is that the DIALS people are working actively towards achieving this theoretical objective, which would have the kinds of benefits you describe (e.g. you can detect outliers more readily and you don't need to anticipate how long your crystal will last).  However, in practice, you can run into problems.  For instance, indexing and post-refinement require detecting spots on the detector.  If the algorithm for detecting spots only looks at single images, and if you reduce the photons per image, you eventually reach a point where no spots are detected.  So spot detection algorithms somehow have to be updated.  Similar issues apply to determining accurate reflection profiles.  

Anyway, while there's a gap between theory and practice, it would be best not to reduce the photons per image too far.  Perhaps someone from the DIALS team could comment on how far one might go with current software?

Best wishes,

Randy Read

On 3 Nov 2015, at 10:18, Jonathan Davies <[log in to unmask]> wrote:

Thanks Jacob

-------- Forwarded Message --------
Subject:RE: [ccp4bb] New Rule for PADs
Date:Tue, 3 Nov 2015 01:05:19 +0000
From:Keller, Jacob <[log in to unmask]>
To:Jonathan Davies <[log in to unmask]>


>Has there been any further discussion on this?

Only a resounding silence…!


>I don't fully understand why one would require such a high multiplicity, would there be any significant difference between a dataset with a multiplicity of 100 compared to one with a multiplicity of 20 say, or even 10 (apart from specific cases such as sulphur SAD)?

I was thinking that for estimations of errors, which can be important, this would be very good.

>Would the attenuation also possibly affect the resolution, i.e. worse signal to noise in high resolution shell?

No, not at all, and this is exactly my point. With PADs, there is zero readout noise, so it does not matter whether you collect your photons in 10 frames or 1000 frames: the signal is the same. The benefit is huge, however, in that reciprocal space is sampled evenly as a function of radiation dose, whereas in the usual method, crystals are damaged by the time the dataset reaches full completeness.

Thanks for your interest—you could post this to the list, and it might engender some interesting discussion.

Jacob



On 26/10/15 19:35, Keller, Jacob wrote:
[log in to unmask]" type="cite" class="">
How about a new rule for data collected on pixel area detectors (Pilatus etc):

Attenuate to ensure multiplicity/redundancy greater than 100?

JPK

*******************************************
Jacob Pearson Keller, PhD
Looger Lab/HHMI Janelia Research Campus
19700 Helix Dr, Ashburn, VA 20147
email: [log in to unmask]
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------
Randy J. Read
Department of Haematology, University of Cambridge
Cambridge Institute for Medical Research      Tel: + 44 1223 336500
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