Per-particle ctf estimation

closed

#1

Hi All,

I have noticed that, during Local Motion Correction, the log reports that “Particles already have CTF estimates: these will not be modified.” I have a dataset that was collected with a tilted grid, so I’d like to refine the ctf estimate on a per-particle basis. Is there a way to force that to happen during the Local Motion Correction procedure?


#2

To answer my own question in case anyone else wondered, the beta implementation of gctf seems to be appropriate for the purpose.


#3

Local refinement in GCTF suffers from the assumption that nearby particles should have similar defocus. However, they might be on opposite sides of the ice.

In our experience there’s no need to use GCTF to get initial per-particle defocus estimates, and the defocus refinement in cisTEM or Relion (which don’t have any prior on nearby particles, for better or for worse) can still find the correct values as judged by improved map quality.


#4

Good to know. Thanks!