[3dem] 4k x 4k cameras

[Steve Ludtke]

Yes, this is well known, but it isn't related to a specific resolution. That is,
the MTF of the CCD camera is related to the pixel size, so the B-factors will
depend on the magnification used on the microscope. Note that it also depends
strongly on the scintillator you selected for your CCD camera. High sensitivity
cameras will have poorer point spread functions, and hence more falloff in the
MTF. ie - there is a tradeoff between sensitivity and MTF of the camera. This
must be carefully considered when collecting images on CCD. The magnification
should be selected such that you won't have MTF problems at the desired
resolution, but still have sufficient particles within each frame to make
accurate measurement of the defocus and other CTF parameters. When purchasing a
CCD camera you have to decide the purpose of the camera. For relatively high
dose work like single particle analysis, low-sensitivity cameras are better, but
for tomography, you might want higher sensitivity.

----------------------------------------------------------------------------
Steven Ludtke, PhD              |        Baylor College of Medicine
sludtke at bcm.tmc.edu             |     Associate Professor & Co-Director
stevel at alumni.caltech.edu       | National Center For Macromolecular Imaging
V: (713)798-9020                |    Dept of Biochemistry and Mol. Biol.
F: (713)798-1625                |
                                |             Those who Do, Are
http://ncmi.bcm.edu/~stevel     |         The converse also applies

On Fri, 14 Dec 2007, Terje Dokland wrote:

> 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
> > __________________________________________________________________
> > _______________________________________________
> > 3dem mailing list
> > 3dem at ncmir.ucsd.edu
> > https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>
> _______________________________________________
> 3dem mailing list
> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>