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,

-- 
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