Web Icon    Web: CTF Parameters

CTF From Document FIle

The purpose of this operation is to help the user to determine the CTF parameters (Contrast transfer function) based on 1D rotationally averaged power spectrum of a micrograph. Further details on this operation are available in the SPIDER manual page for TF and TF D.

The operation initially solicits name of a document file containing 1D rotationally averaged power spectrum. The power spectrum should be placed in the first column of this document file. A batch program that estimates power spectra for a series of micrographs is included in the techniques page/recon/mr.html : Three Dimensional Reconstruction of Single Particle Specimens using Reference Projections.

After the document file name is provided, the user specifies the following input parameters:

The user can now interactively adjust the following parameters to obtain plots.

How to proceed: the defocus value and amplitude contrast (usually set to 0.1) have to be adjusted such that the vertical lines (corresponding to locations of zero crossings of the CTF) coincide with the minima of the power spectrum. Usually the initial 10% of the power spectrum curve length oscillates widely and can be ignored by setting the plot cutoff.

Last update: 7/05/2000     ArDean Leith