[3dem] 4k x 4k cameras
Terje Dokland
dokland at uab.edu
Fri Dec 14 10:13:29 PST 2007
Hi,
Thanks for starting this discussion. It brings up a question/concern
that I have been pondering for a while and wanted to ask the 3DEM
mailing list.
We have the Gatan Ultrascan 4k x 4k, which replaced the Ultrascan 2k
x 2k that originally came with the microscope (a Tecnai F20) in April
this year. It generally works great, although I don't think the DM
software is very good. Anyway, that's a different issue. My main
concern is this:
We have now collected data sets on the same samples using both film
and CCD (on both 2k and 4k cameras) and I have made the following
observation: When I fit the CTF curve to the data using CTFIT from
the EMAN suite the CCD data (both 2k and 4k cameras) has consistently
higher B factors (200-300) than the film data (100-200). The electron
dose is generally the same in both cases and the pixel size is
similar (around 2A). My interpretation of this is that the frequency
response of the CCD is not as good as that of the film.
I realize that this is not a rigorous test, since the actual
particles analyzed are not identical, and there could be other
differences between the samples. But I am concerned.
I wonder if others have made similar observations and if somebody has
an explanation for these differences. Is this an inherent feature of
the CCD camera? Is there a problem with these specific cameras? Am I
comparing apples to oranges? Could somebody suggest a more rigorous,
standardized test that I can make to compare the frequency falloff
for film versus CCD in our setup? Any suggestions/comments would be
very welcome.
Terje Dokland
On Dec 14, 2007, at 11:59 AM, Eva Nogales wrote:
> Dear all,
>
> We are considering the purchase of a 4k x 4k camera and would like
> to hear from the field how the different models/companies are doing
> in your own experience. All comments would be most appreciated!
>
> Eva Nogales
> --
> __________________________________________________________________
>
> Eva Nogales
> Howard Hughes Medical Institute
> Molecular and Cell Biology Department
> QB3, Stanley Hall 708C
> University of California, Berkeley
> Berkeley, CA 94720-3220
>
> Phone: (510) 642-0557 Fax: (510) 666-3336
> URL: cryoem.berkeley.edu
> (510) 666-3334 Teresa Tucker, Assistant to Eva Nogales
>
> Professor, UC Berkeley and Lawrence Berkeley Natl. Lab
> __________________________________________________________________
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