Hi Oli,
I am facing the same behaviour in some of my dataset. The common feature is the high concentration of relatively large particles per image and as you describe. I get a nice Thon rings at “low” frequencies, a sort of gap around 6-4A and then again good fitting beyond 4 (Using ctffind4.1.5 over movies). Somehow I could get around this using the per-particle CTF correction from Gctf however the improvement after the reconstruction is not dramatic.
I wonder if excluding the fit for the solvent may help or perhaps applying a annular mask to the power spectrum in order to to keep the two frequency regimes separated.
Any thoughts on that?
Cheers,
Edo
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Edoardo D'Imprima
PhD Student
Max Planck Institute of Biophysics
Structural Biology Department
Max-von-Laue Straße 3
60438 Frankfurt am Main
Germany
Tel: +49 (0) 69 6303 3015
> On 16 Jun 2017, at 22:41, Oliver Clarke <[log in to unmask]> wrote:
>
> Hi all,
>
> When collecting RyR data (and I guess likewise for other large particles), the number of particles per image is relatively low, and the Thon rings (from protein, not solvent) are consequently relatively weak (see attached), compared to samples of small proteins where we have 100s of particles per micrograph.
>
> I’m wondering if this may be limiting resolution due to poor CTF correction, and whether going to one mag lower to increase the number of particles per micrograph, but using super res to keep a similar effective pixel size, might be a viable strategy to improve power spectra for better CTF correction.
>
> Does anyone have any experience/thoughts re this approach? Or is it dumb for reasons that aren’t occurring to me on a friday afternoon?
>
> Cheers
> Oli
>
> <gc_mic_00046_ctf_avrot.jpg>
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