It definitely could be the pin, assuming that projects in from the opposite
side as the beamstop shadow. Although the crystal is a major source of
background scatter, and obviously the pin cannot cast a shadow in that light,
air scattering is also significant, and the air at the tip of the collimator
(exit slits or whatever) will cast a shadow of your pin.
If that is the case the data in the shadow should not be compromised,
as the pin is not in the path of the diffracted beamlets. Might even
have higher I/sigma due to decreased background, if the integration
program can fit the gently-varying background and subtract it out.
But looking at the image I don't see any spots in the shadow,
so maybe its actually cast by something between the crystal
and the plate?
Ed
Alejandro Buschiazzo wrote:
Dear ccp4bb users,
I have a question that concerns a problem with data collection (not
directly related to CCP4). It might be a really stupid mistake I'm
making...
I'm attaching a diffraction frame where, as you can easily see, there is
an annoying shadow (on purpose the contrast on the image has been forced
to highlight the problem). The shadow doesn't correspond to the cryo
nozzle, since the nozzle is set coming in from the same direction as the
attachment of the beamstop, i.e. right opposite to the shadow.
The detector is an image plate (Mar345), and this problem appears when
collecting at high-ish resolution (say better than 1.8).
I wonder if someone has encountered a similar problem...I've been
playing around for a while now, unfortunately not finding a way out.
could it be associated to the metallic pin of the cryo-loop on which the
xtal is actually mounted? I thought if the loop is rather short, at high
diffraction angles this could actually be a shadow generated by the tip
of the metallic rod....they're pretty much conventional pins though, and
I didn't step into this type of problem before. In any case how could I
handle this, if it were the actual cause of this anomaly?
I tried to adjust the collimator end, or even change it trying other
sizes as well, with no success.
I'll certainly appreciate any help / suggestions!
Best regards,
------------------------------------------------------------------------
