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<p style="margin-top:0;margin-bottom:0">Is the phase shift due to the PP treated as constant (relative to the unscattered beam) above 20 Angstrom resolution (and as unknown at very low resolution)?</p>
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<p style="margin-top:0;margin-bottom:0">Philip</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> 3dem <3dem-bounces@ncmir.ucsd.edu> on behalf of Wim Hagen <hagen@embl.de><br>
<b>Sent:</b> 27 May 2019 15:49:33<br>
<b>To:</b> microscopy@microscopy.com; 3dem@ncmir.ucsd.edu<br>
<b>Subject:</b> Re: [3dem] CTF-correction with phase plate</font>
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<div class="" style="word-wrap:break-word; line-break:after-white-space">Dear Philip,
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<div class="">I am not aware of any CTF-estimation package that applies the correct model for a Volta phase plate. The Volta patch to give the un-scattered beam its phase shift has a size I the back focal plane, meaning it gives a soft cut-on, see figure 2B
in <a href="https://elifesciences.org/articles/23006" class="">https://elifesciences.org/articles/23006</a> . The workaround for this is to start fitting CTF past 20Å. This then requires a nice thin particle-crowded sample to stil successfully fit enough Thon-rings
to estimate defocus, astigmatism and the additional phase shift parameter.</div>
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<div class="">Best,</div>
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<div class="">Wim</div>
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<div class="">On 27. May 2019, at 13:16, Philip Köck <<a href="mailto:Philip.Koeck@ki.se" class="">Philip.Koeck@ki.se</a>> wrote:</div>
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<div class="" style="margin-top:0px; margin-bottom:0px">Dear all.</div>
<div class="" style="margin-top:0px; margin-bottom:0px">I'm trying to find out how the contribution of a hole free or Volta phase plate to the PCTF is described mathematically in various packages that are used for cryo-EM of macromolecules.</div>
<div class="" style="margin-top:0px; margin-bottom:0px">The physics behind it would also be of interest.</div>
<div class="" style="margin-top:0px; margin-bottom:0px">Does anybody know a reference or have some material that can be shared?</div>
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