Hi everyone, could anyone explain what might have caused this curve? I would really appreciate it
What is the sample? What defocus range did you collect across? Have you done any Global CTF refinement? This can happen if you do not have a good range of defoci… it’s too rapid to be pixel calibration or beam tilt related I think.
Thank you. The sample is HSP60. The defocus range is −1.0 to −2.4 μm. I did not perform global CTF refinement. We are trying to run global CTF refinement.
I guess you applied symmetry during refinement? When refining with higher symmetry (icosahedral in my case) I see similar effects on my FSC curve. The density looks fine for me nonetheless.
@jasonhe; OK, there’s nothing there which screams “likely cause”. How many particles?
@DerLorenz; imposing icosahedral symmetry makes the FSC oscillate? 
@rbs_sci Yes, for me it does. At least when refining with a small amount of particles. I work with very difficult and sparse icosahedral particles that are a nightmare to purify. Thus, I end up with little particles.
Below is a FSC from 100 particles refining to 3.8Å.
The reconstruction is reasonable and corresponds to the reported resolution. Here some sidechains:
Co-purified ribosomes refine very high and have picture perfect FSC curves.
This wobbling is reproducible for different particles with different microscopes - all with very little particles contributing to the reconstructions.
Probably due to incomplete defocus coverage with that few particles?
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That would be why. As Oli says, not enough of a range of defoci.
edit: also, depending on virus, some of it might be minor flexibility in e.g. P-domains. We have a few viruses where dips around 8, 6 and 4 Ang due to different levels of flexibility can manifest (which is usually resolved with symmetry expansion and classification and/or focussed refinement).
Ok makes sense. Thanks for the insight 
- this was bothering me. I hope to get some more particles in the future and see if it fixes the FSC curves.
Regarding the inital post by @jasonhe, I would conclude that is likely not symmetry related. Checking other of my FSCs none of them looks as wavy as yours. Sorry for hijacking the thread.