[3dem] 4k x 4k cameras

[Steve Ludtke]

I think you'd have to characterize that statement as general principle rather
than specific advice. Gatan has a lot of detailed data on this, but
they consider much of it proprietary, so I fear you'll have to talk to them for
hard numbers (or repeat the research :^) ). That is, there is some tradeoff
involved between sensitivity and point spread. Since most people spending the
money for a 4K CCD camera are also either doing or considering doing both
single particle and tomography, the CCD makers do have a 'standard'
configuration, but there are more options if you think getting close to Nyquist
is more important than collecting every electron, for example.

----------------------------------------------------------------------------
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 Mon, 17 Dec 2007, Bob Grassucci wrote:

> Hi Steve,
>     I am intrigued by your comment that you should select a low sensitivity camera for single particle work since it is generally
> higher dose than tomography. The CCD manufacturers assume that everyone in the biological EM community wants a high sensitivity
> scintillator.   Do you have a feeling about what dose rate the switch over is advisable?  Thanks,
>     Regards,
>     Bob
>
> Steve Ludtke wrote:
>
>  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
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>  --
> ********************************
>
> -Robert Grassucci-
> Howard Hughes Medical Institute
> Wadsworth Center Empire State Plaza
> Albany, NY 12201-0509
> bobg at wadsworth.org
> Phone: (518)474-5821
> Fax: (518)486-2191
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