Estimating the output from ctffind

Submitted by Grigory on Thu, 2011-06-23 10:33

Forums

ctffind & ctftilt

Dear Niko,
I have a small question regarding ctffind. Please find attached output from the program.
I'm actually interested in two things: should I change ResMax for better correlation between ctf fit and power spectrum and the second one is what are additional grey circles in ctf fit on top of the image?
Thank you in advance.

Alexis Thu, 2011-06-23 11:19

Hi Grigory,

Niko is travelling, so I'll do my best to answer your question.

You could change ResMax to some lower value, so that only regions of the spectrum where Thon rings are visible in your data are used during the fit. This may improve the quality of the fit slightly by effectively removing some more noise.

If I understand your description correctly, you are wondering what the grey concentric rings are, on the left hand side, "on top of" the simulated/fitted CTF function. These are aliasing artefacts, which are inevitable when sampling & displaying CTFs with very narrow oscillations (narrower than 1 pixel). Nothing to worry about.

HTH
Alexis