Hi Marta,
This bump (the valley, not the hill) is common and not an indication of processing issues. It may arise from the reduced scattering power of proteins in this frequency range.
Best regards,
Basil
> Am 26.11.2020 um 15:16 schrieb Marta Sawicka <[log in to unmask]>:
>
> Dear cryo-EM folks,
>
> I have observed a strange bump in FSC curves, which always occurs in a region between 5.5-4.5 A. I see the same pattern regardless of a protein I work with and data processing strategy. Having read what has been already discussed in relation to spikes in the FSC curves I suspect a significant error in the pixel size to cause this bump. Also, having compared maps of the same protein coming from different microscopes, I needed to rescale the pixel size by approximately 5% to get a correct fit. Based on the RELION wiki entry on the pixel size issues, I have redone CtfRefine with estimation of the 4th order aberrations followed by another run to recalculate per-particle defocus. As far as I understand this should make things consistent with a wrong pixel size and after I feed a correct “absolute” pixel size in PostProcessing, I should get FSC curves without the bump. However, this is not the case and the FSCs look pretty much exactly the same. Is there something fundamental that I am missing here? I would appreciate any ideas/suggestions.
>
> Many thanks,
> Marta
>
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