> Let's say you collect data (or rather indices) to 1.4 Ang but the real > resolution is 2.8 Ang and you use all the data in refinement with no > resolution cut-off, so there are 8 times as many data. Then your 15 > mins becomes 2 hours - is that still acceptable? It's unlikely that > you'll see any difference in the results so was all that extra > computing worth the effort? > > Now work out the total number of pixels in one of your datasets (i.e. > no of pixels per image times no of images). Divide that by the no of > reflections in the a.u. and multiply by 15 mins (it's probably in the > region of 400 days!): still acceptable? Again it's unlikely you'll > see any significant difference in the results (assuming you only use > the Bragg spots), so again was it worth it? > > What matters in terms of information content is not the absolute > intensity but the ratio intensity / (expected intensity). As the data > get weaker at higher d* I falls off, but so does <I> and the ratio I / > <I> becomes progressively more unreliable at determining the > information content. So a zero I when the other intensities in the > same d* shell are strong is indeed a powerful constraint (this I > suspect is what Wang meant), however if the other intensities in the > shell are also all zero it tells you next to nothing. > > -- Ian >
I envisioned a process of iteration through the various stages of processing, so still using integration, scaling, etc. to reduce data before refinement, but maybe feeding back model-based information to inform the processing of the images. Something like, Refmac says to Mosflm: "kill frames 1100-1200: they're too radiation-damaged." But I like your idea of using all the pixels--that would be the ultimate, wouldn't it! Actually, the best would be to have the refinement already going when collecting data, and informing which frames to take, and for how long! In a couple years that too will take no time at all, but then again, we'll probably have atomic-precision real-time in vivo microscopes by then anyway, and crystallography will have become an (interesting!) historical curiosity... JPK ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: j-kell...@northwestern.edu *******************************************
