[3dem] 4k x 4k cameras

[Terje Dokland]

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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