[ccp4bb]: Indexing: Summary

["Jim Naismith" <naismith@st-andrews.ac.uk>]

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Dear All,
		Thank you very much for your help.
Once we had the C2221 cell accurately we could force this in our other data. As
many of you predicted and I had hoped. So we are all happy. 


However, I did a little PM.

The reason it did not get the high symmetry first time round was slight errors
in centre and detector distortion. This coupled to mosaic spread of 1 degree,
0.2 oscillations and 2.8 data is a tough call for any program. 

Once these were set to the refined value, and we took a few frames with known
cell we could make autoindexing work. 

Previously MOSFLM would not stably refine with the high symmetry cell.
Before you read any comments re manufacturers warranty. DENZO had exactly the
same problem.

Both methods of indexing are happy with P21 for integration with the rough
values, where the long axis is perpendicular to the rotation axis. Through
post-refinement they get a P21 cell which easily transforms into C222 cell. The
R-merge of this transformation is only marginally higher than correct processing
in C222 in MOSLFM. This tells us MOSFLM does a good job in processing with P21
cell, DENZO data seems likewise to be re-merged (not exhaustively tested). Would
we have noticed our error, I am sure we would! :) But we might have wasted some
time first.

Any lessons? None but the old saw
Use a cheater for long cell axis if your data is difficult. 

I spent over an hour making a pin of the right length and centring etc. At the
ESRF this was a lot of data time but it has helped us solve the structure.

Best
Jim


James H. Naismith                | Research mailto:naismith@st-and.ac.uk
Professor of Chemical Biology    | Teaching mailto:jhn@st-and.ac.uk
BBSRC Career Development Fellow  |
Centre for Biomolecular Sciences | Office: 1334-463792 (24 hr)
The North Haugh                  | Fax   : 1334-467229
The University                   | Lab   : 1334-467245
St. Andrews                      | In UK     add  0 to start of number
Fife Scotland, U.K., KY16 9ST    | www     http://speedy.st-and.ac.uk/