Dear Bharat,
The quality of Thon rings obtained from individual particles is usually
not sufficient to obtain high quality defocus estimates (the notable
exception being very large objects like viruses). [This is why gctf
implements a neat algorithm for estimating local defocus by including
neighboring particles in the computation of the amplitude spectrum (cf
Eqn 10 of the paper).] I assume the same would be true of any
"resolution" estimate derived from the quality of the CTF fit.
I am sure with some scripting effort, this could be tested with any CTF
fitting program and I suppose if the estimates were deemed reliable
enough (perhaps because large areas surrounding particles were used),
you might be able to identify areas with bad local charging artefacts,
ice thickness variations, local beam-induced motion etc. I'd certainly
be interested in hearing whether this works (and helps) in practice.
Cheers,
Alexis
On 02/24/2017 03:49 PM, Bharat Reddy wrote:
> Dear All,
>
> Is there a way to use CTFFind or Gctf to do an individual particle
> resolution estimate? I know Gctf can do per particle defocus estimate
> using --do_local_refine, however in the resulting local star file, it
> does not have the resolution estimate. The big idea is that this might
> be a way to exclude poor particles from an otherwise good micrograph or
> vice versa.
>
> Cheers,
> BR
> _________________________________
> Bharat Reddy, Ph.D.
> Perozo Lab, University of Chicago
> Email: [log in to unmask]
> Tel: (773) 834 - 4734
|