[3dem] Cs question

[Joshua Dickerson]

Hi David,

There's been a lot of excellent advice already, but I thought I'd add my
experience.

If you want to measure the Cs, the magnification/pixel size has to be
accurately calibrated first. There are several ways of doing this that work
pretty well. I like to use the lattice spacing in a thin gold foil, such as
a HexAuFoil grid, since you can calibrate all the high mags accurately with
just a few images per magnification. There is a program to do this and a
paper comparing several pixel size calibration methods here:
https://urldefense.com/v3/__https://www.mrc-lmb.cam.ac.uk/crusso/magCalEM/index.html__;!!Mih3wA!F7gjnTy38fid9HhbLpIbXtKJirVZwehFZ7mOBOXX0rZBHNlZGlSYabbxOHTGf916JKfm4QRvX3JSvs0IOEYpEZCBElw$ 

Once you have the pixel size, you can use CTF refinement as others have
suggested. If you also calibrate your beam-tilt coils, which can also be
done using gold, you can also measure the Cs using beam-tilt-induced image
shifts in a method described here
https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/0304399191901583__;!!Mih3wA!F7gjnTy38fid9HhbLpIbXtKJirVZwehFZ7mOBOXX0rZBHNlZGlSYabbxOHTGf916JKfm4QRvX3JSvs0IOEYpUkG2rFk$ 

>From my experience, the manufacturer provided Cs value has always been
accurate, and apparent errors have been pixel size calibration errors.

Best wishes,
Josh

On Mon, Feb 16, 2026 at 1:07 PM Morgan, David Gene via 3dem <
3dem at ncmir.ucsd.edu> wrote:

> Hi,
>
> For those of you who have used any of the image processing programs to
> refine the Cs value for your microscope, how does the refined value compare
> to what the manufacturers claim?
>
> As I understand it, the manufacturers simply calculate a Cs value for each
> microscope/pole piece model.  I guess I have always assumed that those
> values are relatively accurate, but I don't really have any data to support
> that.  Nor am I certain what would constitute "relatively accurate."
>
> Any thoughts would be appreciated.  Thanks.
>
> --
>
> NOTE:  my email has changed to dagmorga at iu.edu.
>              Email to dagmorga at indiana.edu will stop being
>              forwarded later this year.
>
>     politics is more difficult than physics.
>                                              A. Einstein
>
>             David Gene Morgan
>         Electron Microscopy Center
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