<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear Philip,<div class=""><br class=""></div><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><div class=""><br class=""></div><div class="">Best,</div><div class=""><br class=""></div><div class="">Wim</div><div class=""><div><br class=""><blockquote type="cite" class=""><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><br class="Apple-interchange-newline"><div class=""><div id="divtagdefaultwrapper" dir="ltr" style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class=""><div style="margin-top: 0px; margin-bottom: 0px;" class="">Dear all.</div><div style="margin-top: 0px; margin-bottom: 0px;" class="">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 style="margin-top: 0px; margin-bottom: 0px;" class="">The physics behind it would also be of interest.</div><div style="margin-top: 0px; margin-bottom: 0px;" class="">Does anybody know a reference or have some material that can be shared?</div></div><div style="margin: 0px; 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