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Dear 3dem community,</div>
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During an application session on our Glacios with a ThermoFisher Engineer we had the opportunity to try the multiposition acquisition scheme '("<b>Off-axis Multi-shot acquisition</b>") within
<b>Tomo5</b>.</div>
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The software worked well for <b>tracking </b>positions, even far from the tilt axis.</div>
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But when I went to check the average <b>Defocus</b> of each tilt image among the <b>
full tilt series</b>, the result was disappointing.</div>
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I observed a huge <b>drift from the Target defocus</b> while going to negative tilt angles or positive tilt angles.</div>
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Here is an example of the measured defocus in regards of tilt angle values within a Tilt Serie being acquired at off-axis position:</div>
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<img id="x_Image_x0020_2" style="width: 361.49pt; height: 203.24pt; max-width: 1252px; min-width: auto; min-height: auto;" width="481" height="270" data-outlook-trace="F:0|T:1" src="cid:0a78022c-26c7-47dd-9ed9-1a5bac5d5dfe"></div>
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So it seems that the z displacement of the off-axis position is not well taken into account for target defocus compensation.</div>
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Is it an expected behaviour ?</div>
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On the other side I noted that the <b>tilt angles</b> registered (from -60 to +60) are inverted regarding the
<b>global convention</b> (Cf: <a href="https://urldefense.com/v3/__https:/wiki.dynamo.biozentrum.unibas.ch/w/index.php/Tilt_angle_convention__;!!HLrAl2XzZ3iCLg!EtUHtX4pBonU0MJaEHxIHwMRqPioLC-0rGu3X0vcdN0BN8CDvbS0Hb6WbucrNiGuxtVYE2m2vpfeKNAEXhHNbn_aVdbfAahNks3bVg$" target="_blank" id="OWA0673481e-0848-830d-7f23-12a86688f055" class="OWAAutoLink" rel="noopener noreferrer" data-auth="NotApplicable" data-linkindex="0">
https://wiki.dynamo.biozentrum.unibas.ch/w/index.php/Tilt_angle_convention</a>). My tilt image being tagged -60 correspond to +60 according to the convention and so on.</div>
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Indeed when I tested the defocus from left side and right side of a tilt image it shown an inconsistent behaviour in regards with the convention.</div>
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In the meantime, the<b> tilt axis angle</b> registered in the mdoc files show a suspicious negative sign: <b>-90.30</b>.</div>
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If then we consider the tilt axis angle to be rather<b> +89.70</b> (inverted orientation of the tilt axis), the registered tilt angles become consistent.</div>
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So here I am wondering if the disappointing defocus behaviour during off-axis tilt serie acquisition could be due to a wrong recorded orientation of the tilt axis.</div>
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Does it make sense ? Does anyone here had already faced such situation ?</div>
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Thank you for your help.</div>
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<b>Julien Maufront</b></div>
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Research Engineer – Cryo-Electron Microscopy Platform</div>
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<b><i>Institut Curie – Research Center</i></b></div>
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Molecular Microscopy of Membranes</div>
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