Dear Bryan,
As Mark van Raaij pointed out you have complete
flexibility in specifying the images to be used in autoindexing or in
cell refinement.
However, the default behaviour is to use the first image and a second
image that is as close as possible to 90 degrees away for
autoindexing, and for cell refinement a small wedge of data starting
with the first image and a second small wedge as close as possible to
90 degrees away. In more recent versions, three or four wedges will be
selected for cell refinement in low symmetry space groups (monoclinic /
triclinic using images at 0, 90 and one or 2 wedges in between) as
this gives better determined parameters.
The use of two images (or sets of images) well separated in phi
(ideally 90 degrees) allows the most reliable determination of the
cell parameters, especially for low symmetry space groups. In
particular, for monoclinic or triclinic space groups, when using a
single image it is possible to obtain an indexing solution that
predicts that image very well but is in fact incorrect, and will not
predict images far away in phi.
Best wishes,
Andrew
On 17 Mar 2011, at 18:44, Bryan Lepore wrote:
I seem to have noticed that (i)mosflm can index on one image, or two
images that are not related by 90 degrees. also, cell refinement
sometimes splits up a set of frames into maybe 3 or four segments of
e.g. a few degrees each. and of course, I can set it based on frames
90 degrees apart.
reason I ask is that i thought mosflm's modus operandi was based on
frames in general being related by 90 degrees - is mosflm simply
written differently or is there some criteria it uses to make these
settings, or something else...
-Bryan
