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CCP4BB  May 2007

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Subject:

FW: [ccp4bb] image plate shadow

From:

"Nave, C (Colin)" <[log in to unmask]>

Reply-To:

Nave, C (Colin)

Date:

Fri, 4 May 2007 14:30:33 +0100

Content-Type:

text/plain

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text/plain (55 lines)

Alejandro,
As others have said, the most likely explanation is the attenuation of the air scatter by the sample holder. There is no sharp edge to the shadow which indicates the source of scatter is along an extended path. Ed Berry pointed out that he didn't see spots in the shadow. This might be because the threshold you used to illustrate this brought the spots plus background too low to see but you can check this. As Ed says, the data might actually be better in this region.

The fun thing to do is to print out the image on transparent sheet at approximately the same size as the image on the plate itself. Move the detector back and put the sheet in its place at the correct distance. If there is room to get your head in, you can then view from the far side of the image through to the crystal mount, collimator etc. All should then become clear (provided that is you can still see through the sheet).

Colin
 

-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]]On Behalf Of
Alejandro Buschiazzo
Sent: 03 May 2007 23:52
To: [log in to unmask]
Subject: [ccp4bb] image plate shadow


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

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