I am struggling to perform the CTF fitting due ice contamination. In a large proportion of my images, the CTF model fits the strong signal from the ice rather than the weaker Thon rings of the sample. I was wondering if there is a way to exclude the ice rings from the CTF correction (like in X-ray diffraction data)? I am using CTFFIND4 in Relion 3.1.
I have attached two examples of CTF fit, one where the fitting worked and one where it didn't.
Thank you for your help and best wishes,