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Re: [ccp4bb] How to reduce no. of overlaps

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999
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Subject: FW: endotoxin removal
From: Jerry McCully for-crystallizaiton {- at -} HOTMAIL {- dot -} COM
Date: 2012-03-07
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From: Paul Smith paul {- at -} PALADINSCIENTIFIC {- dot -} COM
Date: 2012-03-07


Subject: Re: How to reduce no. of overlaps
From: "Edward A {- dot -} Berry" BerryE {- at -} UPSTATE {- dot -} EDU
Date: 2012-03-07

Jim Pflugrath wrote:
> In addition to reducing the beam divergence, you may wish to use a
> smaller beam size by using a smaller collimator or making the slits
> smaller. A smaller crystal can also help to spatially separate the Bragg
> spots as can moving the detector closer to the crystal. Yes, closer to
> the crystal. This is not intuitive, but arises since modern homelab
> beams are not parallel but are diverging from a focal point near the
> sample position. It is just something else you may wish to try.
>
But the pattern is also diverging from a point at the sample?

I'm guessing the focus point is somewhere between the crystal
and the detector, so by moving the detector closer you are better
approximating "focus on the detector" rather than "focus on the crystal"?

With a home source one probably has room for a Huber goniometer with
arcs, or better yet one of those goniometers that allows rotation
up to 90* about a point at the crystal, so the crystal doesn't move
out of the cold stream as you rotate.

One can also cheat on the mosaicity during integration by fixing
it at a small fraction of the true mosaicity. This is called
"cutting off the wings" or more euphemistically "peak height
sampling". The accuracy will suffer, but not as much as you
might expect- probably because if spot profiles are pretty
similar, the the height at peak is a good measure of peak
volume.

eab

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999
Previous message:
Subject: FW: endotoxin removal
From: Jerry McCully for-crystallizaiton {- at -} HOTMAIL {- dot -} COM
Date: 2012-03-07
Next message:
Subject: Re: REFMAC Riding Hydrogens
From: Paul Smith paul {- at -} PALADINSCIENTIFIC {- dot -} COM
Date: 2012-03-07



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