many thanks for the suggestions!
I recall my request for help yesterday: how to deal with a semicircular
shadow on my IP images, starting at some angle extending all the way to
the rim of the detector plate, opposite to the single attachment point
of the beamstop (it's not a Mylar-held one), while collecting data at
~1.5 angstroms (xtal2detector dist 100mm) with a Mar345.
I've been trying several ideas today. What I can say now is that the
"obstacle" appears to be really between the xtal and the detector (not
only the background is reduced by a factor of 5 on the shaded area, but,
no matter how I fiddle around with the contrast, there really are NO
diffraction spots at all). Of course, being this the case, I suppose I'm
actually loosing information altogether....(what would the integration
do if I don't include a mask: I guess it will try to integrate spots
which are not actually there....so ~0 intensity spots? at 40%
completeness, collection still in progress, Rmerge vs resol does show
some particular rise matching the resolution where the shadow starts,
not sure if it's significant; at the same time, I'm not having any
rejections at the scaling step...?!; I admit I don't know the type of
figures I should actually be looking for in the Chi and Chi**2 vs
detector position analyses in scala...)
With the same pin (magnetic CryoCap from Hamtpon; not the copper ones),
I actually translated in z to try and move away the metallic rod of the
mounted cryoloop from the beam path......no success.
My conclusion for the moment: the shadow comes from the the metallic pin
that directly holds the cryoloop (no other obstacle is evident!), which
in this particular case is actually very close to the crystal (the nylon
loop is apparently too short!). Before I didn't use Hampton: is this
actually a common problem with these mounted cryoloops? If this is the
case, I don't have now much choice (other than changing crystal of
course...and throwing away this particular loop by the way!).
If these conlusions are valid, no matter how narrow I go with the
collimator mouth, the shadow will always be there (it appears to be the
geometric relation between crystal and cryopin base....) ...am I right?
If I find some way of solving this annoying artifact, I'll certainly
post it.
I hope I "integrated" the different suggestions and thanks again!
further comments are very much welcome
Best regards,
--
Alejandro Buschiazzo, PhD
Research Scientist
Laboratory of Structural Biology
Pasteur Institute of Montevideo
Mataojo 2020
Montevideo 11400
URUGUAY
Phone: +5982 5220910 int. 120
Fax: +5982 5220910 int. 111
