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<div>Dear Henning,</div>
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<div>The image distortion associated with losing high resolution info, in general speaking, could be caused by lens astigmatism or asymmetric aberration, detector pixels asymmetrically fading away seems to be unlikely. Because the image you showed was from
post GIF detector, the distortion could be generated by obj lens, intermediate/projection lens or the GIF lens system, or a local electric magnetic field. </div>
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<div>You may test few things to identify the distortion source:</div>
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<li>If you have a camera before GIF, you may record an image at the same pixel size as the K2 post GIF, this will tell you if the obj lens has any problem.</li><li>If the distortion only appears at post GIF K2, you can adjust the stigmator at near focus to minimize the obj. lens astigmatism on K2 at the magnification you use, this may give you a hint if the demagnifying for GIF caused any problem which is FEI’s job
to fix it.</li><li>Find an open area(vacuum) and switch to diffraction mode using over 2m camera length and over focusing C2/spread out beam intensity more, change the focus, which is the obj/projection/intermediate focus knob on the right panel, from over to under focus,
watch the direct beam bright center changing on the screen camera and adjust the project/intermediate lens astigmatism until you see a Benz logo shape as shown in the attachment. This step may need a person is more familiar with electron diffraction.</li><li>If the distortion is still there, it indicate the distortion may be from Gatan lens system, you can tune the GIF system or ask Gatan to do it for you.</li><li>If none of above the tests cannot identify the source, you may check if there is very local and small field generated by dirty or contamination near the camera</li><li>check the K2 chip? </li></ol>
<div>Sorry I’m running out of idea and hope you can fix the problem soon,</div>
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<div>Best regards,</div>
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<div>Dan</div>
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<div>Dan Shi</div>
<div>Janelia Research Campus, HHMI</div>
<div>19700 Helix Dr, Ashburn</div>
<div>VA 20147, USA </div>
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<span style="font-weight:bold">From: </span>3dem <<a href="mailto:3dem-bounces@ncmir.ucsd.edu">3dem-bounces@ncmir.ucsd.edu</a>> on behalf of Henning Stahlberg <<a href="mailto:henning.stahlberg@unibas.ch">henning.stahlberg@unibas.ch</a>><br>
<span style="font-weight:bold">Date: </span>Thursday, May 11, 2017 at 9:08 AM<br>
<span style="font-weight:bold">To: </span>3dem <<a href="mailto:3dem@ncmir.ucsd.edu">3dem@ncmir.ucsd.edu</a>><br>
<span style="font-weight:bold">Subject: </span>[3dem] Request for help to find source of resolution loss in cryo-EM<br>
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Hi,<br class="">
<br class="">
We have a strange problem on one of our instruments (Titan Krios with Quantum-LS GIF and K2 Summit in counting mode).<br class="">
When recording images at low mag (1.04 A/px for the 4k images) and low-dose conditions of a partly devitrified sample, and compute the FFTs, we can see the 3.7A ice ring and also the second-order 2.1A ice ring, sometimes a third-order ring in the corners at
1.7A resolution.<br class="">
We recently observed a resolution loss visible in the FFTs only in the vertical direction, shown by an amplitude decay in the upper and lower quarter of the FFTs. <br class="">
However, while the 3.7A ring shows that anisotropic resolution loss, the 2.1A ring is still isotropically present. An example image is attached.<br class="">
<br class="">
Does anybody have an idea what could cause such a behavior?<br class="">
<br class="">
Thanks,<br class="">
<br class="">
Henning.<br class="">
<br class="">
<br class="">
<br class="">
<div class="">Henning Stahlberg, PhD<br class="">
Prof. for Structural Biology, C-CINA, Biozentrum, University Basel<br class="">
Mattenstrasse 26 | D-BSSE | WRO-1058 | CH-4058 Basel | Switzerland<br class="">
<a href="http://c-cina.org" class="">http://c-cina.org</a> | Tel. +41-61-387 32 62<br class="">
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