Finding Defocus with Ctfplotter for Two Example Tilt Series

(IMOD 4.9)

University of Colorado, Boulder

 

This document will guide you through running Ctfplotter to find defocus for two different tilt series, one where the signal is of the CTF is very strong and one where it is weak.  It will explain some of the most important aspects of the process.  For more details, consult the Guide to Ctfplotter, which fully explains each aspect of the interface and also has screen shots based on these two data sets.  Labels in the Etomo or 3dmod interface are shown in Bold, and entries in fields are shown in italics.

 

Determining Defocus in a Tilt Series from a K2 Camera:

This tilt series, from Cindi Schwartz, is of a flagellum of a Giardia cell, taken with a K2 camera on a Krios microscope at Janelia Farm.  The total dose was 26 electrons/square Angstrom.  Images were taken in superresolution mode with an exposure time of 0.5 sec to avoid having to save and align subframes, and reduced by a factor of 4 with antialiasing.  With this protocol, they may have somewhat better high-frequency information than a typical tilt series taken in counting mode without binning, so the power spectra may be particularly good here.

Determining Defocus in a Low-defocus Tilt Series from a CCD camera:from a CCD camera: