Re: [ccp4bb]: MOSFLM, XDS, DENZO - conversion of crystal missetting angles ?

[Harry Powell <harry@mrc-lmb.cam.ac.uk>]

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On Mon, 19 Feb 2001, Phraenquex VD wrote:

> Mosflm?  In my experience, mosflm can use a rather large number of
> frames... I think I once went as far as 20.  When I index, I use two
> images at least 45 degrees apart as a matter of course, it tends to save a
> lot of agony. 

Due to an error (feature/bug/typo) in an array dimension you can use up 20
images for the "old-style" Kabsch indexing but only 10 for the "new-style"
FFT indexing. Mea culpa... the fix will appear in v6.11 (I'll put the fix
on the Mosflm help pages so if you have the source you can fix it
yourself...). 

> 
> Weak images, too, often don't seem to bother it, I've successfully indexed
> images using just 10 spots, all worse than 4A.
> 
> The only thing that does seem to matter is the beam position -- and that
> applies to all programs I've used.  The old mosflm indexing algorithm (the
> one you get when you say "no" when asked whether to use DPS), that one
> seems a bit more robust about the beam centre, but then you need strong
> images and certainly include spots from several images widely separated in
> phi. 
> 

You need to know the beam position to within half the minimum spot
separation for any autoindexing to work or the indexing will be incorrect
even if it seems to work. 

> Also be careful about that, the x and y convention is switched between
> some programs.  I can never remember which it is, but I think where mosflm
> uses (x,y), denzo and d*trek use (y,x).  Or something like that, try both. 

There's still a jiffy program around which will do the conversion from
Denzo to Mosflm indexing (from the days before the "new-style"
indexing"); see ftp://ftp.mrc-lmb.cam.ac.uk/pub/pre/denzo2mosflm.f


Harry 
-- 
Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
Road, Cambridge, CB2 2QH