[3dem] CTF Correction with Spider

[William Baxter]

As we have used it, the Gaussian envelope halfwidth (GEH) is an
empirically derived value used to obtain an estimate of the envelope
function. It can be estimated using the output of SPIDER's TF ED command
with the graphical tool ctfmatch
(www.wadsworth.org/spider_doc/spire/doc/guitools/ctfmatch/ctfmatch.html).

The effect of GEH can be essentially turned of by using  a large value 
(e.g., 1000) , which sets this parameter to one at all frequencies. The
envelope can then be modeled using other parameters such as source size
and defocus spread.

Bill Baxter
The Wadsworth Center
Albany, NY

xim9 at pitt.edu wrote:
> Dear All,
>
> I use the software, SPIDER to correct CTF. In order to compute the phase
> contrast transfer function (Spider operations, TF C or TF C3), GAUSSIAN
> ENVELOPE HALFWIDTH need to be known. I have two questions about it.
>
> (1) what is the range of Gaussian envelope halfwidth for FEG TEM?
> (2) how to estimate this value?
>
> Does anybody Know this?
>
> Thanks,
>
> Xin Meng
>
>
>
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>   



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