[3dem] ctf-fitting with phase plate

[Daniel Asarnow]

Hi Philip,
It's just an additional phase added to the argument of the sine and cosine
(amplitude contrast) functions in the CTF. See e.g. Eqn 2. in the CTFFIND4
paper <http://www.sciencedirect.com/science/article/pii/S1047847715300460>.
It is not dependent on spatial frequency - every frequency gets the same
additional phase shift due to the plate. Here is a gist
<https://gist.github.com/asarnow/b47c7f1c7aab1d292c10a8c03dd1b6b8> of a
Python function for evaluating the CTF, which is much the same as those in
Relion or cisTEM.

I'm not sure if anyone knows the sign of the accumulated charge, but I
imagine electrons are deposited and the charge is negative. Maybe someone
else here has a better physically intuitive argument one way or the other.

Best,
-da

On Sat, Mar 23, 2019 at 5:23 AM Philip Köck <Philip.Koeck at ki.se> wrote:

> Hi.
>
> I've been looking for information on the contribution of a self charging
> phase plate (hole free or Volta)
> to the argument of the CTF in weak amplitude and phase approximation for
> homogenous specimens.
>
> What function is used to describe the phase shift as a function of spatial
> frequency?
>
> Also, is the charge produced by the TEM-beam positive or negative (or
> both)?
>
> All the best,
>
> Philip
>
>
>
> *När du skickar e-post till Karolinska Institutet (KI) innebär detta att
> KI kommer att behandla dina personuppgifter. *Här finns information om
> hur KI behandlar personuppgifter
> <https://ki.se/medarbetare/integritetsskyddspolicy>.
>
>
> *Sending email to Karolinska Institutet (KI) will result in KI processing
> your personal data.* You can read more about KI’s processing of personal
> data here <https://ki.se/en/staff/data-protection-policy>.
> _______________________________________________
> 3dem mailing list
> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20190323/41541cc3/attachment.html>