[3dem] phosphur thickness and CCD resolution

[Bill Tivol]

On Apr 10, 2008, at 1:59 PM, acheng at scripps.edu wrote:

>   Does anyone have any idea how much resolution loss we might get when
> the CCD camera sensitivity is increased by about two-fold?
>
>   We recently replace the CCD chip and the phosphur on top of our  
> 4k Gatan
> camera.  Gatan technician said that the phosphur is thicker, and we
> observe that our camera sensitivity has gone up.  The question  
> would be
> whether this will affect the MTF or the usable resolution of our  
> camera by
> similar factor, worse or not as much.


Dear Anchi,
	When we measured this--crudely; we just looked at how many pixels it  
took to go from bright to dark across an edge--we found ~50% increase  
in point-spread width.  Whether this makes usable resolution better  
or worse depends on several factors, such as S/N, image contrast,  
whether the pixel size is small compared to resolution, and other  
properties of both specimen and camera.  In our case, we found better  
results with a brighter screen, but YMMV.
Yours,
Bill Tivol, PhD
EM Scientist
Electron Cryo-Microscopy Facility
Broad Center, Mail Code 114-96
California Institute of Technology
Pasadena CA 91125
(626) 395-8833
tivol at caltech.edu

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