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<div>Hi Tommi,</div>
<div>You may try a couple of experiments to identify the offset source,</div>
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<li>Set 0 um and 0 degree beam/image shift for focus mode from exposure mode with different magnification, focus image on either mode and switch to another one, if there is any offset focus on the second mode, the defocus/over focus could be from none-parallel
beam. If both modes has the same magnification, the problem may be from normalization which would be only action during switching mode.</li><li>Set beam offset at different distance and different orientations and record images, such as 90 degree away, then compare to the 0 defocus image recorded at exposure mode, this experiment may tell you if there is flatness issue or other source.</li></ol>
<div>As long as the offset is consistent, FEI or other automation software may be able to adjust the lens program to compensate it because Krios seems to have no such problem.</div>
<div>Good luck,</div>
<div>Dan</div>
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<span style="font-weight:bold">From: </span>Tommi White <<a href="mailto:whitetommi@gmail.com">whitetommi@gmail.com</a>><br>
<span style="font-weight:bold">Date: </span>Monday, April 27, 2015 5:52 PM<br>
<span style="font-weight:bold">To: </span>"<a href="mailto:3dem@ncmir.ucsd.edu">3dem@ncmir.ucsd.edu</a>" <<a href="mailto:3dem@ncmir.ucsd.edu">3dem@ncmir.ucsd.edu</a>><br>
<span style="font-weight:bold">Subject: </span>[3dem] Low Dose Focus/Exposure<br>
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<div>Dear 3DEM.<br>
<br>
Perhaps the community can assist with this issue we are struggling with. In Low Dose on our Tecnai F30, the Low Dose focus image has a different defocus value (using FFT) versus Low Dose Exposure.
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I have been checking this on a relatively flat cross-grating (not cryo) specimen. I set LD exposure to be zero defocus (with focus knob), but when I switch over to LD focus (~ 3 micron away on tilt axis) the image is defocused (~ -2 micron).
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I believe there is some 200 kV procedure alignment that must not be set properly - but am not quite sure which one...any suggestions on what to tweak to get this exposure/focus area reflecting the same defocus?<br>
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Thanks for any suggestions...<br>
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Tommi<br>
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Tommi A. White, Ph.D.<br>
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Associate Director, Electron Microscopy Core Facility<br>
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Assistant Professor of Biochemistry<br>
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University of Missouri<br>
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W125 Veterinary Medicine<br>
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Columbia, MO 65211<br>
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573-882-8304<br>
<a href="http://emc.missouri.edu">http://emc.missouri.edu</a><br>
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